sfe: Periodically import approved rate limit override tickets

[beautifulentropy]

Add a periodic background job to the SFE with the following responsibilities:

• Search for Zendesk tickets that have a status of "open" and an reviewStatus of "approved"
• Process even numbered, odd numbered, or all Zendesk tickets depending on JSON configuration; this allows us to process tickets simultaneously in both DCs without the two SFEs having to coordinate locks
• Re-validate fields from Zendesk tickets, perform any transformations as necessary (e.g. Account URI to ID)
• If any ticket fields fail validation transition to Zendesk ticket to "pending" and leave a private comment concerning the issue
• Write each approved and valid override request to the overrides table, in the enabled state
• If any requested override is already administratively disabled, notify SFE via a private comment and transition the ticket to "pending"
• Finally, close the ticket with a public comment that contains the relevant information

Closes #8166

[jprenken]

Nit: Implementing this as two "M of N" settings (with the same underlying modulo bucketing logic) is pretty simple and would allow a lot more flexibility. But this all/even/odd mode is already implemented and will work fine for us, so NBD.

[jsha]

Generally looks great! A few small tweaks, and one proposed refactoring for processTicket.

[jsha]

As a possible followup: I'd love to split UpdateTicketStatus into UpdateTicketPublic and UpdateTicketPrivate, since boolean fields can make it easy to make copy-paste mistakes. Definitely not required as part of this PR.

[beautifulentropy]

I like that idea. I had to write tests to make sure that we got the intended result and it should keyed me in to the idea that these two should be a little more separate.

[github-actions]

@beautifulentropy, this PR appears to contain configuration and/or SQL schema changes. Please ensure that a corresponding deployment ticket has been filed with the new values.