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)
Until now we had a load test with 50k unique JWTs signed with symmetric key.
This commit adds a new load test with 10k JWTs signed with RSA 4096.
Existing -k jwt parameter was changed to -k jwt-hs-50k.
New test is run with -k jwt-rsa-10k parameter.
Additionally a new parameter --jwtcache=off was added to turn off JWT caching in the above load tests.
This change introduces a PostgREST.Auth.Jwt module containing JWT validation functions.
The reason to extract them from Auth is to enable JwtCache module to reuse them without introducing module dependency cycle.
