Integrate Gitaly CountCommits pseudo-revisions support in Rails application

Summary

Gitaly's CountCommits RPC now supports pseudo-revisions like --branches, --tags, --not, --all, and --glob through a new revisions field. This brings CountCommits in line with ListCommits functionality.

Related Gitaly MR: gitaly!8349 (merged)

Changes in Gitaly

The Gitaly CountCommits RPC has been extended with:

• A new repeated bytes revisions field in CountCommitsRequest
• Support for pseudo-revisions using AllowPseudoRevision() validation
• Backward compatibility with existing revision and all fields
• The new revisions field takes precedence when provided

Example usage:

• Count commits in all branches: revisions=["--branches"]
• Count commits excluding a ref: revisions=["HEAD", "--not", "main"]

Integration Tasks

• Update Gitaly protobuf definitions to include the new revisions field
• Identify places in Rails codebase where CountCommits is called
• Update Gitlab::Git::Repository to expose the new revisions parameter
• Add support for passing multiple revisions and pseudo-revisions
• Update relevant GraphQL or REST API endpoints
• Add tests for the new functionality

Benefits

• More efficient commit counting across multiple refs
• Support for complex revision queries
• Consistency with ListCommits API patterns
• Better performance for multi-reference operations