Handle namespace/project deletion events in Geo cursor

We now log project deletion events on the Geo tracking DB. We need to start using this to delete directories that are no longer needed.

How this might work:

1. Cursor looks for projects that use the old path
2. If any exist, mark those projects as dirty
3. Otherwise, schedule the directory for deletion (e.g. rename and purge after some time)

In a DR scenario, we may want to keep deleted projects for longer than the primary, which is 5 minutes.

mentioned in issue #2828 (closed)

mentioned in issue #2838 (closed)

changed milestone to %9.5

Here are my thoughts on this. We can do this one of two ways:

1. Use the existing repo sync mechanism to look for dirty projects, and check that they are not deleted
2. Introduce something else that looks for deleted projects

I'm favoring the first option because that means we don't need yet another query to figure out which projects are deleted, and it's just part of the sync process. @dbalexandre, what do you think?

Simple iteration went in via !2452 (merged).

closed