[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>

build/release.mk

@@ -76,7 +76,7 @@ package:
 	@# Resource directories
 	mkdir -p $(DIST_PATH)/config
 	cp -L config/README.md $(DIST_PATH)/config
-	OUTPUT_CONFIG=$(PWD)/$(DIST_PATH)/config/config.json go generate ./config
+	OUTPUT_CONFIG=$(PWD)/$(DIST_PATH)/config/config.json go run ./scripts/config_generator
 	cp -RL fonts $(DIST_PATH)
 	cp -RL templates $(DIST_PATH)
 	rm -rf $(DIST_PATH)/templates/*.mjml $(DIST_PATH)/templates/partials/