Increase provider lookup cache TTL to 10 seconds
Increase provider lookup cache TTL to 10 seconds

Tested locally with TTL values of:
- 2 seconds
- 5 seconds
- 10 seconds

The benefit really started showing at 10 seconds, where >50% of lookups
hit the cache rather than the database.

For graphs see https://github.com/alphagov/notifications-api/pull/3075#issuecomment-750836404

alphagov/notifications-api,alphagov/notifications-api