feat: JWT cache implementation based on sieve algorithm (#4084)

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)

src/PostgREST/Observation.hs

@@ -60,6 +60,8 @@ data Observation
   | HasqlPoolObs SQL.Observation
   | PoolRequest
   | PoolRequestFullfilled
+  | JwtCacheLookup Bool
+  | JwtCacheEviction
 
 data ObsFatalError = ServerAuthError | ServerPgrstBug | ServerError42P05 | ServerError08P01
 
@@ -151,6 +153,10 @@ observationMessage = \case
     "Trying to borrow a connection from pool"
   PoolRequestFullfilled ->
     "Borrowed a connection from the pool"
+  JwtCacheLookup _ ->
+    "Looked up a JWT in JWT cache"
+  JwtCacheEviction ->
+    "Evicted entry from JWT cache"
   where
     showMillis :: Double -> Text
     showMillis x = toS $ showFFloat (Just 1) (x * 1000) ""