Create WAL event tracker table to track all the WAL events.

Design Doc: https://docs.google.com/document/d/14oZ5ssY28hvJaQD_Jg9kWX7LfUKUyyU2PCA93PPzVko/edit#

Create wal event tracker table to track WAL events. Whenever we roll the WAL, we will save the WAL name, WAL length, region server, timestamp in a table.