[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>

api4/config_test.go

@@ -721,11 +721,11 @@ func TestMigrateConfig(t *testing.T) {
 	})
 
 	th.TestForSystemAdminAndLocal(t, func(t *testing.T, client *model.Client4) {
-		f, err := config.NewStore("from.json", false, false, nil)
+		f, err := config.NewStoreFromDSN("from.json", false, false, nil)
 		require.NoError(t, err)
 		defer f.RemoveFile("from.json")
 
-		_, err = config.NewStore("to.json", false, false, nil)
+		_, err = config.NewStoreFromDSN("to.json", false, false, nil)
 		require.NoError(t, err)
 		defer f.RemoveFile("to.json")
 

api4/user_test.go

@@ -5523,6 +5523,9 @@ func TestThreadSocketEvents(t *testing.T) {
 	os.Setenv("MM_FEATUREFLAGS_COLLAPSEDTHREADS", "true")
 	defer os.Unsetenv("MM_FEATUREFLAGS_COLLAPSEDTHREADS")
 
+	th.ConfigStore.SetReadOnlyFF(false)
+	defer th.ConfigStore.SetReadOnlyFF(true)
+
 	th.App.UpdateConfig(func(cfg *model.Config) {
 		*cfg.ServiceSettings.ThreadAutoFollow = true
 		*cfg.ServiceSettings.CollapsedThreads = model.COLLAPSED_THREADS_DEFAULT_ON