Add MigrateNamespace and MigrateTagTemplate as post database update
maintenance operations.
Bug: T367207
Change-Id: I7676f9ce4bef59febc463d897cb26d47347a3968
* Move MySQL files into subfolder
* Simplify onLoadExtensionSchemaUpdates hook by using variable for dbType
* Document what MW version patches were added
Bug: T353922
Change-Id: I4b87481163121047619d173675747feef4d8ede1
This hook is not allowed to have a service, so before we can add
services to the main Hooks class, it needs to be split out.
Change-Id: Ia7b4b8bf7c91ebb851c5de9f0f54f56b0993bf83