[MM-32234] Fix config.json getting reset (#16805)

* Add support for read-only config stores

* Allow read/write config store for plugin commands that require it

app/config.go

@@ -46,6 +46,9 @@ func (a *App) EnvironmentConfig() map[string]interface{} {
 }
 
 func (s *Server) UpdateConfig(f func(*model.Config)) {
+	if s.configStore.IsReadOnly() {
+		return
+	}
 	old := s.Config()
 	updated := old.Clone()
 	f(updated)

app/options.go

@@ -43,9 +43,9 @@ func StoreOverride(override interface{}) Option {
 // or a database connection string. It receives as well a set of
 // custom defaults that will be applied for any unset property of the
 // config loaded from the dsn on top of the normal defaults
-func Config(dsn string, watch bool, configDefaults *model.Config) Option {
+func Config(dsn string, watch, readOnly bool, configDefaults *model.Config) Option {
 	return func(s *Server) error {
-		configStore, err := config.NewStore(dsn, watch, configDefaults)
+		configStore, err := config.NewStore(dsn, watch, readOnly, configDefaults)
 		if err != nil {
 			return errors.Wrap(err, "failed to apply Config option")
 		}

app/server.go

@@ -210,7 +210,7 @@ func NewServer(options ...Option) (*Server, error) {
 		if err != nil {
 			return nil, errors.Wrap(err, "failed to load config")
 		}
-		configStore, err := config.NewStoreFromBacking(innerStore, nil)
+		configStore, err := config.NewStoreFromBacking(innerStore, nil, false)
 		if err != nil {
 			return nil, errors.Wrap(err, "failed to load config")
 		}

app/server_test.go

@@ -384,7 +384,7 @@ func TestSentry(t *testing.T) {
 
 		s, err := NewServer(func(server *Server) error {
 			configStore, _ := config.NewFileStore("config.json", true)
-			store, _ := config.NewStoreFromBacking(configStore, nil)
+			store, _ := config.NewStoreFromBacking(configStore, nil, false)
 			server.configStore = store
 			server.UpdateConfig(func(cfg *model.Config) {
 				*cfg.ServiceSettings.ListenAddress = ":0"
@@ -435,7 +435,7 @@ func TestSentry(t *testing.T) {
 
 		s, err := NewServer(func(server *Server) error {
 			configStore, _ := config.NewFileStore("config.json", true)
-			store, _ := config.NewStoreFromBacking(configStore, nil)
+			store, _ := config.NewStoreFromBacking(configStore, nil, false)
 			server.configStore = store
 			server.UpdateConfig(func(cfg *model.Config) {
 				*cfg.ServiceSettings.ListenAddress = ":0"