Merge the DrydockLease workers into a single worker

Summary:
Ref T9252. This is the same as D14201, but for lease stuff instead of resource stuff.

This one is a little heavier but still feels pretty reasonable to me at the end of the day (worker is <1K lines and has a ton of comment stuff).

Also fixes a few random bugs I hit in the task queue.

Test Plan:

• Restarted some Harbormaster builds, saw them go through cleanly.
• Released pre-activation resources/leases.
• Probably still kinda buggy but I'll iron the details out over time.

Logs are starting to look somewhat plausible:

{F855747}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9252

Differential Revision: https://secure.phabricator.com/D14202