Add a function DatabaseHolder::updateMigratingTenantAccessBlockersForDatabasesMatching(StringData dbPrefix).

The method should check if MigratingTenantAccessBlockerByPrefix has an entry for the passed-in prefix, and if so, iterate all databases. For each database, if the database's name matches the prefix, it should set the database's MigratingTenantAccessBlocker decoration to the entry's MigratingTenantAccessBlocker.

This method is similar to DatabaseHolder::getNamesWithConflictingCasing.