[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>

cmd/gotosocial/common.go

@@ -64,11 +64,17 @@ func preRun(a preRunArgs) error {
 // context, after initializing any last-minute things like loggers etc.
 func run(ctx context.Context, action action.GTSAction) error {
 	log.SetTimeFormat(config.GetLogTimestampFormat())
-	// Set the global log level from configuration
+
+	// Set the global log level from configuration.
 	if err := log.ParseLevel(config.GetLogLevel()); err != nil {
 		return fmt.Errorf("error parsing log level: %w", err)
 	}
 
+	// Set global log output format from configuration.
+	if err := log.ParseFormat(config.GetLogFormat()); err != nil {
+		return fmt.Errorf("error parsing log format: %w", err)
+	}
+
 	if config.GetSyslogEnabled() {
 		// Enable logging to syslog
 		if err := log.EnableSyslog(