Follow up from Auto Fix MVC - backend

This is an issue to track all remaining non-blocking work for the auto-fix feature. It should be addressed preferably while the feature is under the feature flag.

• Refactor Security::Cofiguration::SaveAutoFixService- add ServiceResponse as the responce and process errors
• !48679 (comment 464217635) Add Security::VulnerabilitiesFindingFinder entity to preload feedback data in AutoFixService see this comment
• add migration for make bot confirmed !49167 (comment 464281322) this should be addressed before feature flag is turned off
• Add background migration for ProjectSecuritySetting to add this entity to existing projects
• add label Gitlab-auto-fix for auto created merge requests