OzoneManager Cache

In this Jira, we shall implement a cache for Table.

As with OM HA, we are planning to implement double buffer implementation to flush transaction in a batch, instead of using rocksdb put() for every operation. When this comes in to place we need cache in OzoneManager HA to handle/server the requests for validation/returning responses.

This Jira will implement Cache as an integral part of the table. In this way users using this table does not need to handle like check cache/db. For this, we can update get API in the table to handle the cache.

This Jira will implement:

1. Cache as a part of each Table.
2. Uses this cache in get().
3. Exposes api for cleanup, add entries to cache.

Usage to add the entries in to cache will be done in further jira's.