Advanced Search unsupported migration should be a preflight check

Proposal

We currently have an Advanced Search migration which pauses indexing for unsupported search versions. This should be converted from a migration to a preflight check used in the Elastic::MigrationWorker to support future Search version upgrades and deprecation work. Information about behavior should be added to the documentation for GitLab administrators.

Note: the migration currently checks for known compatible version. This could cause an issue when future versions get released that may be compatible but we do not know. The migration worker preflight check should check for known incompatible versions only.