API: Move AllowedReactions endpoint into GetGenneralUI endpoint + creat new swagger section settings (#11854)

* move Setting function into its own package

* swagger add&use new section "settings"

* move api AllowedReactions into general UI-Settings endpoint

* prepare TEST

* lint

modules/structs/settings.go

@@ -9,3 +9,8 @@ type GeneralRepoSettings struct {
 	MirrorsDisabled bool `json:"mirrors_disabled"`
 	HTTPGitDisabled bool `json:"http_git_disabled"`
 }
+
+// GeneralUISettings contains global ui settings exposed by API
+type GeneralUISettings struct {
+	AllowedReactions []string `json:"allowed_reactions"`
+}