Use ServiceResponse in Boards::CreateService

What does this MR do?

It refactors Boards::CreateService and returns ServiceResponse object.

This returned object will be later used in create board mutation, similarly as eg. destroy board mutation

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.