MM-10658 Change config fields to pointers (#9033)

* MM 10658 Change config fields to pointers (#8898)

* Change fields of config structs to pointers and set defaults

MM-10658 https://github.com/mattermost/mattermost-server/issues/8841

* Fix tests that go broken during switching config structs to pointers

MM-10658 https://github.com/mattermost/mattermost-server/issues/8841

* Apply changes of current master while switching config structs to pointers

MM-10658 https://github.com/mattermost/mattermost-server/issues/8841

* Fix new config pointer uses

* Fix app tests

* Fix mail test

* remove debugging statement

* fix TestUpdateConfig

* assign config consistently

* initialize AmazonS3Region in TestS3TestConnection

* initialize fields for TestEmailTest

* fix TestCheckMandatoryS3Fields

app/plugin_api.go

@@ -477,7 +477,7 @@ func (api *PluginAPI) GetFileInfo(fileId string) (*model.FileInfo, *model.AppErr
 }
 
 func (api *PluginAPI) GetFileLink(fileId string) (string, *model.AppError) {
-	if !api.app.Config().FileSettings.EnablePublicLink {
+	if !*api.app.Config().FileSettings.EnablePublicLink {
 		return "", model.NewAppError("GetFileLink", "plugin_api.get_file_link.disabled.app_error", nil, "", http.StatusNotImplemented)
 	}