Improve Data Repository documentation

[dtaimanov]

There are several things absent in Data Repositories documentation chapter:

• [x] io.jmix.core.repository.ApplyConstraints annotation usage (ability to use UnconstrainedDataManager)
• [x] JmixDataRepositoryContext parameter (see https://github.com/jmix-framework/jmix/issues/2490)
• [x] Update Features part with newly added improvements: https://github.com/jmix-framework/jmix/issues/2523, https://github.com/jmix-framework/jmix/issues/2131
• [x] Clarify FetchPlan and Hints priority when different values set in method name/query and method parameters (see https://github.com/jmix-framework/jmix/issues/2490)

[sukhova]

Also describe how to create repositories in Studio. Information about this is available in Support for Data Repositories of What's new for 2.1