[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>

config/utils.go

@@ -4,7 +4,9 @@
 package config
 
 import (
+	"bytes"
 	"encoding/json"
+	"fmt"
 	"reflect"
 	"strings"
 
@@ -14,6 +16,11 @@ import (
 	"github.com/mattermost/mattermost-server/v5/utils"
 )
 
+// marshalConfig converts the given configuration into JSON bytes for persistence.
+func marshalConfig(cfg *model.Config) ([]byte, error) {
+	return json.MarshalIndent(cfg, "", "    ")
+}
+
 // desanitize replaces fake settings with their actual values.
 func desanitize(actual, target *model.Config) {
 	if target.LdapSettings.BindPassword != nil && *target.LdapSettings.BindPassword == model.FAKE_SETTING {
@@ -191,20 +198,11 @@ func stripPassword(dsn, schema string) string {
 	return prefix + dsn[:i+1] + dsn[j:]
 }
 
-func IsJsonMap(data string) bool {
+func isJSONMap(data string) bool {
 	var m map[string]interface{}
 	return json.Unmarshal([]byte(data), &m) == nil
 }
 
-func JSONToLogTargetCfg(data []byte) (mlog.LogTargetCfg, error) {
-	cfg := make(mlog.LogTargetCfg)
-	err := json.Unmarshal(data, &cfg)
-	if err != nil {
-		return nil, err
-	}
-	return cfg, nil
-}
-
 func GetValueByPath(path []string, obj interface{}) (interface{}, bool) {
 	r := reflect.ValueOf(obj)
 	var val reflect.Value
@@ -249,3 +247,15 @@ func GetValueByPath(path []string, obj interface{}) (interface{}, bool) {
 	}
 	return nil, false
 }
+
+func equal(oldCfg, newCfg *model.Config) (bool, error) {
+	oldCfgBytes, err := json.Marshal(oldCfg)
+	if err != nil {
+		return false, fmt.Errorf("failed to marshal old config: %w", err)
+	}
+	newCfgBytes, err := json.Marshal(newCfg)
+	if err != nil {
+		return false, fmt.Errorf("failed to marshal new config: %w", err)
+	}
+	return !bytes.Equal(oldCfgBytes, newCfgBytes), nil
+}