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)

docs/references/observability.rst

@@ -201,6 +201,40 @@ pgrst_db_pool_max
 
 Max pool connections.
 
+.. _jwt_cache_metrics:
+
+JWT Cache Metrics
+-----------------
+
+Metrics related to the :ref:`jwt_caching`.
+
+pgrst_jwt_cache_requests_total
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+======== =======
+**Type** Counter
+======== =======
+
+The total number of JWT cache lookups.
+
+pgrst_jwt_cache_hits_total
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+======== =======
+**Type** Counter
+======== =======
+
+The total number of JWT cache hits.
+
+pgrst_jwt_cache_evictions_total
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+======== =======
+**Type** Counter
+======== =======
+
+The total number of JWT cache evictions.
+
 Traces
 ======