[feature + performance] add JSON logging format (#4355)

# Description

Adds JSON logging as an optional alternative log output format. In the process this moves our log formatting itself into a separate subpkg to make it more easily modular, and improves caller name getting with some calling function name caching.

## Checklist

- [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.
- [x] 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`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4355
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

internal/log/init.go

@@ -23,7 +23,8 @@ import (
 	"strings"
 )
 
-// ParseLevel will parse the log level from given string and set to appropriate LEVEL.
+// ParseLevel will parse the log level from
+// given string and set to appropriate LEVEL.
 func ParseLevel(str string) error {
 	switch strings.ToLower(str) {
 	case "trace":
@@ -44,16 +45,22 @@ func ParseLevel(str string) error {
 	return nil
 }
 
-// EnableSyslog will enabling logging to the syslog at given address.
-func EnableSyslog(proto, addr string) error {
-	// Dial a connection to the syslog daemon
-	writer, err := syslog.Dial(proto, addr, 0, "gotosocial")
-	if err != nil {
-		return err
+// ParseFormat will parse the log format from
+// given string and set appropriate formatter.
+func ParseFormat(str string) error {
+	switch strings.ToLower(str) {
+	case "json":
+		SetJSON(true)
+	case "", "logfmt":
+		SetJSON(false)
+	default:
+		return fmt.Errorf("unknown log format: %q", str)
 	}
-
-	// Set the syslog writer
-	sysout = writer
-
 	return nil
 }
+
+// EnableSyslog will enabling logging to the syslog at given address.
+func EnableSyslog(proto, addr string) (err error) {
+	sysout, err = syslog.Dial(proto, addr, 0, "gotosocial")
+	return err
+}