Enabling Audit event when default branch changes for a project

What does this MR do?

Currently Gitlab does not provide any change in project settings in Audit events. This is particularly interested if the project is in a SOX scope and the user change any of the project settings. This MR basically adds an entry in audit events if the default branch is changed.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.