sfe: Add background job that regularly imports approved rate limit overrides from Zendesk

[beautifulentropy]

• Search for Zendesk tickets that have a status of open and an reviewStatus of approved
• Process Even, Odd, or All depending on JSON configuration, this allows us to process tickets simultaneously in both DCs without the two SFEs having to coordinate locks
• Import and validate fields from Zendesk tickets
• Transform AccountURI (web UI and Zendesk) to AccountID (overrides database table)
• If any fields fail validation we need to report this back to SRE in the form of a non-public comment in the ticket (change status to "pending")
• Write each approved override to the overrides table in the enabled state
• Finally, close the ticket with a public comment that contains the relevant information