Improve local cache and prefer local reads

[avinassh]

Till now, DurableWAL used Storage Server for finding page versions. If the local cache's max_frame_no is same as storage server's and if a txn's max_frame_no is less or same as cache's max_frame_no, then all reads and writes can proceed using local data itself. Do note that writes from a stale primary will be rejected anyways, since we handle conflicts at Storage Server.

Currently, there is no replication built and it assumes a single primary writer. So, after write, it updates the local cache. In the future PRs, I will add replication.

What's changed:

• Update the cache after writes
• Use local cache for most operations

What's next:

• A primary can lag anytime, so we need replication or way to quickly bring up the cache to speed
• If the primary is lagging, we switch to remote mode