Split create_wiki_repository method

What does this MR do?

In follow-up MRs, we need to specifically change the group wiki repository storage. At the moment, all that logic is handled by the method create_wiki_repository automatically, and it doesn't allow us to set the repository storage.

In this MR we split the create_wiki_repository's logic and we create the track_wiki_repository that accepts the shard.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Related to #299054 (closed)