Add operations_access_level to project settings API

What does this MR do?

In this MR we add the project feature operations_access_level to the project API endpoints. This way we can retrieve the value and also set it.

All the BE logic has already been merged.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Related to #224698 (closed)