And use :migration tag to use deletion strategy, and to avoid caching tables, and to lock into a particular schema.

Attempting to fix intermittent spec errors `PG::UndefinedTable: ERROR:  relation "public.untracked_files_for_uploads" does not exist`.

with StrongMemoize

In particular, the Omnibus uploads directory is generally a symlink.

`updated_at` is now unnecessary and `created_at` is less useful due to removing the tracked field.

It makes a debugging slightly easier, but is not necessary, and is a waste of resources.

* Hopefully fixes spec failures in which the table doesn’t exist
* Decouples the background migration from the post-deploy migration, e.g. we could easily run it again even though the table is dropped when finished.

So the path on source installs cannot be too long for our column.

And fix the column length test since Route.path is limited to 255 chars, it doesn’t matter how many nested groups there are.

Since duplicate inserts are now ignored.

To process the unhashed_upload_files table.

To create the table, and schedule the background migration that begins the work.