Make vulnerability and feedback creation feature flag agnostic

This MR will make sure we are creating Feedback, state transition and Vulnerability without depending on feature flag so that we can have fallback when we will enable FF to avoid Feedback on read operation.

I have decided to keep these FF checks:

https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/graphql/mutations/security/finding/create_issue.rb#L26

https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/services/vulnerabilities/revert_to_detected_service.rb#L20

https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/services/vulnerabilities/resolve_service.rb#L18

https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/services/vulnerabilities/confirm_service.rb#L18

Related to #378670 (closed)