Issue template for onboarding a new agency (for devs)

[thekaveman]

Related to #2434

As part of the setup process, let's think through what we (the devs) would need from the CS team (e.g. @o-ram) if / when we have more new agencies to set up.

Then encode that in a simple Issue template to make it easy for a CS team member to request a new agency configuration in Benefits.

[indexing]

@thekaveman Given that we have a handful of agencies slated to onboard to Benefits in H1 2025, I propose we prioritize this issue for slush time. El Dorado will likely be the first agency we configure (#2581 ). They are slated to go live in March, so we will likely be working with @mariearaneta to set them up in test beginning in February.

[o-ram]

Great timing @indexing - Marie and I are working on some Benefits onboarding documentation for account managers right now and we were just talking about github issue templates 😄