Prepare OpenProjectService

What does this MR do?

• it refactors common data field classes to concern in order to avoid code duplication
• it creates a basic class for open project integration
• no real functionality yet

Based on gitlab-foss!24888 (closed) (community contribution)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] 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.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done