gRPC's prepared query cache gets out of sync with persistence's query cache

[dougwettlaufer]

The prepared query cache in gRPC does not currently have a cache invalidation mechanism and because of this when a prepared query is removed from the cache in the persistence module it does not also get removed from the gRPC cache.

I was able to reproduce this issue by

1. Create a keyspace and table
2. Execute an insert query on the table
3. Drop the keyspace
4. Recreate the same keyspace and table
5. Try to run the same insert query again and it fails

To resolve this we need to either a) remove the local cache in gRPC or b) add cache invalidation in order to keep the caches in sync.