[MM-32390] Config logic refactor (#17578)

* Replace config generator

* Cleanup

* Some renaming and docs additions to add clarity

* Cleanup logging related methods

* Cleanup emitter

* Fix TestDefaultsGenerator

* Move feature flags synchronization logic out of config package

* Remove unnecessary util functions

* Simplify load/set logic

* Refine semantics and add some test to cover them

* Remove unnecessary deep copies

* Improve logic further

* Fix license header

* Review file store tests

* Fix test

* Fix test

* Avoid additional write during initialization

* More consistent naming

* Update app/feature_flags.go

Co-authored-by: Christopher Speller <crspeller@gmail.com>

* Update config/store.go

Co-authored-by: Christopher Speller <crspeller@gmail.com>

* Update config/store.go

Co-authored-by: Christopher Speller <crspeller@gmail.com>

* Update config/store.go

Co-authored-by: Ibrahim Serdar Acikgoz <serdaracikgoz86@gmail.com>

* Move FF synchronizer to its own package

* Remove unidiomatic use of sync.Once

* Add some comments

* Rename function

* More comment

Co-authored-by: Christopher Speller <crspeller@gmail.com>
Co-authored-by: Ibrahim Serdar Acikgoz <serdaracikgoz86@gmail.com>

app/options.go

@@ -45,7 +45,7 @@ func StoreOverride(override interface{}) Option {
 // config loaded from the dsn on top of the normal defaults
 func Config(dsn string, watch, readOnly bool, configDefaults *model.Config) Option {
 	return func(s *Server) error {
-		configStore, err := config.NewStore(dsn, watch, readOnly, configDefaults)
+		configStore, err := config.NewStoreFromDSN(dsn, watch, readOnly, configDefaults)
 		if err != nil {
 			return errors.Wrap(err, "failed to apply Config option")
 		}