fix: store just the vshard config version

Summary

• fix: store just the vshard config version

This fixes the A-B-A problem which was observed in the issue #763 (closed).

Closes #763 (closed)

• fixup update_instance

• WIP doc comments for govenor steps

• refactor: support passing additional Dml entries to update_instance_request

• Cherry-pick to: 24.4
• Docs follow-up: docs#308 (closed)