MM-28859 Add feature flag managment system using split.io and remove viper. (#15954)

* Add feature flag managment system using split.io and remove viper.

* Fixing tests.

* Attempt to fix postgres tests.

* Fix watch filepath for advanced logging.

* Review fixes.

* Some error wrapping.

* Remove unessisary store interface.

* Desanitize SplitKey

* Simplify.

* Review feedback.

* Rename split mlog adatper to split logger.

* fsInner

* Style.

* Restore oldcfg test.

* Downgrading non-actionable feature flag errors to warnings.

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/helper_test.go

@@ -48,12 +48,9 @@ func setupTestHelper(dbStore store.Store, enterprise bool, includeCacheLayer boo
 		panic(err)
 	}
 
-	memoryStore, err := config.NewMemoryStoreWithOptions(&config.MemoryStoreOptions{IgnoreEnvironmentOverrides: true})
-	if err != nil {
-		panic("failed to initialize memory store: " + err.Error())
-	}
+	configStore := config.NewTestMemoryStore()
 
-	config := memoryStore.Get()
+	config := configStore.Get()
 	if configSet != nil {
 		configSet(config)
 	}
@@ -62,12 +59,12 @@ func setupTestHelper(dbStore store.Store, enterprise bool, includeCacheLayer boo
 	*config.LogSettings.EnableSentry = false // disable error reporting during tests
 	*config.AnnouncementSettings.AdminNoticesEnabled = false
 	*config.AnnouncementSettings.UserNoticesEnabled = false
-	memoryStore.Set(config)
+	configStore.Set(config)
 
 	buffer := &bytes.Buffer{}
 
 	var options []Option
-	options = append(options, ConfigStore(memoryStore))
+	options = append(options, ConfigStore(configStore))
 	options = append(options, StoreOverride(dbStore))
 	options = append(options, SetLogger(mlog.NewTestingLogger(tb, buffer)))