This performs a dark launch compare of the existing implementation
(still in use) for fetching TPA provider configs and a new
implementation, recording metrics on exceptions and mismatches.

The new implementation should have two benefits, once we're switched
over:

- Fix 1+N queries on login page view where the site for each config
  was fetched in a loop (ARCHBOM-1139)
- Don't allow configs with the same key on different sites to
  interfere with each other (regression test added)

The new impl does not use TieredCache, but only the request cache,
which we may want to adjust later.