Adds schema caching capabilities (5s by default) (#2286)

* Adds schema caching capabilities (off by default)

* Use InMemoryCacheAdapter

* Uses proper adapter to generate a cache

* Fix bugs when running disabled cache

* nits

* nits

* Use options object instead of boolean

* Imrpove concurrency of loadSchema

* Adds testing with SCHEMA_CACHE_ON

* Use CacheController instead of generator

- Makes caching SchemaCache use a generated prefix
- Makes clearing the SchemaCache clear only the cached schema keys
- Enable cache by default (ttl 5s)

src/cli/cli-definitions.js

@@ -197,5 +197,10 @@ export default {
     env: "PARSE_SERVER_REVOKE_SESSION_ON_PASSWORD_RESET",
     help: "When a user changes their password, either through the reset password email or while logged in, all sessions are revoked if this is true. Set to false if you don't want to revoke sessions.",
     action: booleanParser
+  },
+  "schemaCacheTTL": {
+    env: "PARSE_SERVER_SCHEMA_CACHE_TTL",
+    help: "The TTL for caching the schema for optimizing read/write operations. You should put a long TTL when your DB is in production. default to 0; disabled.",
+    action: numberParser("schemaCacheTTL"),
   }
 };