[Admin Panel] Make it possible to delete agencies

[lilidworkin]

It's currently possible to delete users via the Admin Panel -- if you hover over the card, a red trash icon appears in the bottom right. If you click it, a confirmation modal appears.

We'd like to add the same behavior for deleting agencies! It should work similarly with the red trashcan and the confirmation modal.

Unfortunately the backend API for this does not exist yet, but for now you can imagine that there will be an endpoint /admin/agency/<id> DELETE, and build everything assuming that will work.

But since that endpoint won't actually work just yet, let's only show the trashcan if the user's role is AgencyTeamMemberRole.JUSTICE_COUNTS_ADMIN -- that way this won't go live yet to anyone besides us!

cc @mxosman