Geo: Document 14.6 unnecessary resyncing due to new verification feature

Problem

From #334550 (comment 887807869):

In 14.6 we added the Verification feature to LFS objects. I wonder if it's like this:

• Upgrade to 14.6
• The primary site starts checksumming LFS objects
• The secondary site starts checksumming LFS objects and comparing them to primary site checksums
• But most LFS objects are not checksummed yet on the primary
• Therefore many or most (but probably not all) LFS objects start "failing" verification on the secondary site
• A failed verification schedules a resync, therefore many or most LFS objects get resynced

This affects at least Uploads also.

Proposal

• Determine what data types are affected => uploads, LFS objects, Pages deployments, and external merge request diffs, see https://about.gitlab.com/releases/2021/12/22/gitlab-14-6-released/#geo-verifies-four-additional-data-types
• Determine what releases are affected => 14.6, 14.7
• Determine a workaround
  • Deploy GitLab 14.5
  • Store files locally, not in object storage, so that verification will occur
  • Create at least a few of each data type: uploads, LFS objects, Pages deployments, and external merge request diffs
  • Disable auto migrate if enabled
  • Upgrade a node with the gitlab-rails service to 14.6
  • Run pre-deployment migrations only
  • Try this potential workaround: Run update SQL queries which mark uploads, LFS objects, Pages deployments, and external merge request diffs as "verified".
  • Finish upgrading to 14.6
  • List the registry tables of affected data types
  • Look for failed verifications or resyncing. There should be none if the workaround was effective.
  • Run queries to mark all the records of affected data types as "pending verification". Mention that this is optional since re-verification will automatically cause verification of everything, eventually.
• Document the problem and workaround in Geo Version-specific Update instructions doc
  • If multiple sections are needed in Geo Version-specific Update instructions doc, then put the problem and workaround in Geo Troubleshooting and link to that.