[feature] Configurable max profile fields (#4175)

# Description

> If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.
>
> If this is a documentation change, please briefly describe what you've changed and why.

Profile fields, right? So I made them a configurable amount and show them on the instance features. Closes #1876

All changes I did are described in the commits. I tried to cover as much as possible, but I don't know this codebase to know what I've missed. I have tested it manually and it works (settings page, `/api/v1/instances`, server-side validation).

Not done:
- An "Add profile fields" button, so that instances with a high profile fields count (e.g. 100) aren't an issue when trying to skip the profile fields (in some form, accessibility)
- Updating the swagger docs that specify a specific amount of profile fields for the updating endpoint (not sure how to proceed with that)
- Unchecked checklist items

## Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: `[ ]` -> `[x]`

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

- [X] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [X] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [X] I/we have written code that is legible and maintainable by others.
- [ ] I/we have commented the added code, particularly in hard-to-understand areas.
- [X] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [X] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Notes about checklist:
- ["Approval" to work on this reference](https://matrix.to/#/!mlPctfMHjyopbOnliM:superseriousbusiness.org/$P0Z1Qmny6GNIgxhre69gll8KSD690HC8nVvNpXmu3nU?via=superseriousbusiness.org&via=matrix.org&via=tchncs.de)
- `golangci-lint run` output ignored due to complaining about ffmpeg and some other code I didn't touch

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4175
Reviewed-by: kim <gruf@noreply.codeberg.org>
Co-authored-by: Jackson <jackson@jacksonchen666.com>
Co-committed-by: Jackson <jackson@jacksonchen666.com>

internal/config/helpers.gen.go

@@ -79,6 +79,7 @@ func (cfg *Configuration) RegisterFlags(flags *pflag.FlagSet) {
 	flags.Int("accounts-registration-backlog-limit", cfg.AccountsRegistrationBacklogLimit, "Limit how big the 'accounts pending approval' queue can grow before registration is closed. 0 or less = no limit.")
 	flags.Bool("accounts-allow-custom-css", cfg.AccountsAllowCustomCSS, "Allow accounts to enable custom CSS for their profile pages and statuses.")
 	flags.Int("accounts-custom-css-length", cfg.AccountsCustomCSSLength, "Maximum permitted length (characters) of custom CSS for accounts.")
+	flags.Int("accounts-max-profile-fields", cfg.AccountsMaxProfileFields, "Maximum amount of profile fields an account can have.")
 	flags.Int("media-description-min-chars", cfg.MediaDescriptionMinChars, "Min required chars for an image description")
 	flags.Int("media-description-max-chars", cfg.MediaDescriptionMaxChars, "Max permitted chars for an image description")
 	flags.Int("media-remote-cache-days", cfg.MediaRemoteCacheDays, "Number of days to locally cache media from remote instances. If set to 0, remote media will be kept indefinitely.")
@@ -206,7 +207,7 @@ func (cfg *Configuration) RegisterFlags(flags *pflag.FlagSet) {
 }
 
 func (cfg *Configuration) MarshalMap() map[string]any {
-	cfgmap := make(map[string]any, 181)
+	cfgmap := make(map[string]any, 182)
 	cfgmap["log-level"] = cfg.LogLevel
 	cfgmap["log-timestamp-format"] = cfg.LogTimestampFormat
 	cfgmap["log-db-queries"] = cfg.LogDbQueries
@@ -257,6 +258,7 @@ func (cfg *Configuration) MarshalMap() map[string]any {
 	cfgmap["accounts-registration-backlog-limit"] = cfg.AccountsRegistrationBacklogLimit
 	cfgmap["accounts-allow-custom-css"] = cfg.AccountsAllowCustomCSS
 	cfgmap["accounts-custom-css-length"] = cfg.AccountsCustomCSSLength
+	cfgmap["accounts-max-profile-fields"] = cfg.AccountsMaxProfileFields
 	cfgmap["media-description-min-chars"] = cfg.MediaDescriptionMinChars
 	cfgmap["media-description-max-chars"] = cfg.MediaDescriptionMaxChars
 	cfgmap["media-remote-cache-days"] = cfg.MediaRemoteCacheDays
@@ -805,6 +807,14 @@ func (cfg *Configuration) UnmarshalMap(cfgmap map[string]any) error {
 		}
 	}
 
+	if ival, ok := cfgmap["accounts-max-profile-fields"]; ok {
+		var err error
+		cfg.AccountsMaxProfileFields, err = cast.ToIntE(ival)
+		if err != nil {
+			return fmt.Errorf("error casting %#v -> int for 'accounts-max-profile-fields': %w", ival, err)
+		}
+	}
+
 	if ival, ok := cfgmap["media-description-min-chars"]; ok {
 		var err error
 		cfg.MediaDescriptionMinChars, err = cast.ToIntE(ival)
@@ -3138,6 +3148,31 @@ func GetAccountsCustomCSSLength() int { return global.GetAccountsCustomCSSLength
 // SetAccountsCustomCSSLength safely sets the value for global configuration 'AccountsCustomCSSLength' field
 func SetAccountsCustomCSSLength(v int) { global.SetAccountsCustomCSSLength(v) }
 
+// AccountsMaxProfileFieldsFlag returns the flag name for the 'AccountsMaxProfileFields' field
+func AccountsMaxProfileFieldsFlag() string { return "accounts-max-profile-fields" }
+
+// GetAccountsMaxProfileFields safely fetches the Configuration value for state's 'AccountsMaxProfileFields' field
+func (st *ConfigState) GetAccountsMaxProfileFields() (v int) {
+	st.mutex.RLock()
+	v = st.config.AccountsMaxProfileFields
+	st.mutex.RUnlock()
+	return
+}
+
+// SetAccountsMaxProfileFields safely sets the Configuration value for state's 'AccountsMaxProfileFields' field
+func (st *ConfigState) SetAccountsMaxProfileFields(v int) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+	st.config.AccountsMaxProfileFields = v
+	st.reloadToViper()
+}
+
+// GetAccountsMaxProfileFields safely fetches the value for global configuration 'AccountsMaxProfileFields' field
+func GetAccountsMaxProfileFields() int { return global.GetAccountsMaxProfileFields() }
+
+// SetAccountsMaxProfileFields safely sets the value for global configuration 'AccountsMaxProfileFields' field
+func SetAccountsMaxProfileFields(v int) { global.SetAccountsMaxProfileFields(v) }
+
 // MediaDescriptionMinCharsFlag returns the flag name for the 'MediaDescriptionMinChars' field
 func MediaDescriptionMinCharsFlag() string { return "media-description-min-chars" }