MM-14439: experimental restrict system admin (#10414)

* api4: break out license and config from system

* app: move some config functions from admin.go to config.go

* add ExperimentalSettings.RestrictSystemAdmin

* forbid various actions to restricted system admin

* update default.json

* fix function names in errors

api4/api.go

@@ -221,6 +221,8 @@ func Init(configservice configservice.ConfigService, globalOptionsFunc app.AppOp
 	api.InitPost()
 	api.InitFile()
 	api.InitSystem()
+	api.InitLicense()
+	api.InitConfig()
 	api.InitWebhook()
 	api.InitPreference()
 	api.InitSaml()