Implement Redis cache for block and mempool data

backend/src/__fixtures__/mempool-config.template.json

@@ -10,6 +10,7 @@
     "AUTOMATIC_BLOCK_REINDEXING": false,
     "POLL_RATE_MS": 3,
     "CACHE_DIR": "__MEMPOOL_CACHE_DIR__",
+    "CACHE_ENABLED": true,
     "CLEAR_PROTECTION_MINUTES": 4,
     "RECOMMENDED_FEE_PERCENTILE": 5,
     "BLOCK_WEIGHT_UNITS": 6,
@@ -127,5 +128,9 @@
     "AUDIT": false,
     "AUDIT_START_HEIGHT": 774000,
     "SERVERS": []
+  },
+  "REDIS": {
+    "ENABLED": false,
+    "UNIX_SOCKET_PATH": "/tmp/redis.sock"
   }
 }