Geo: sync .gitattributes to info/attributes in secondary nodes

What does this MR do?

• Synchronize .gitattributes from default branch to info/attributes in secondary nodes
• Add specs

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

.gitattributes is synced to info/attributes in primary nodes as part of the GitPushService. This is not reflected in secondary nodes yet.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #4101 (closed)