(state-indexer): Bug with indexing epoch validators info

[kobayurii]

The current implementation faces a challenge where information about validators during an epoch in Near operations may undergo changes. The StakeAction, acting as a trigger for these changes, is not properly considered by the indexer. As a result, the indexer neglects to update validator information when StakeAction occurs, leading to incomplete and inaccurate data about validators for that epoch.

In this PR:

1. Configured the system to save comprehensive information about validators at the conclusion of each epoch. This ensures that the indexer captures and indexes the most up-to-date data about validators, eliminating the issue of incomplete information.
2. Added functionality to include information about the last block of the epoch in the indexing process. This addition ensures that the server maintains a complete record of validator information, providing a comprehensive view of the epoch.

[kobayurii]

#159