Changes:
1. Refactoring and some cleanup of JWT handling code:
* Instead of caching AuthResult cache decoded claims (which signature was verified). Validating claims and determining role is done after cache lookup
* Cleaned up API so that usage of it is simplified: lookupJwtCache cache key >>= parseClaims configJwtAud time
* Handling of JwtCacheState initialization and updates of configuration is encapsulated in Auth.JwtCache module
2. Generic high performance (hopefully) scalable, dynamically resizeable cache implementation based on stm, stm-hamt and sieve algorithm. It also integrates with PostgREST measurements infrastructure providing usage stats (ie. hit ratio, evictions count)
The new tests verify that:
- statement_timeout on the authenticator role works to cancel slow statements
- changes to statement_timeout take effect on SIGUSR1
This reuses the old "limited_authenticator" role and adds some plumbing to
allow reliably changing the statement timeout even if the current role is
not functional due to a low statement timeout, and to make tests that modify
the role independent from each other.
- introduce module-wide metapostgrest fixture to have an out-of-band way to
manipulate the database, without having to spin up extra postgrest instances
per test
- reset statement_timeout at the start of the respective tests
