Healthcheck endpoint to return isBootstrap information

When the indexer is perform a bootstrap operation, we shall let the FE aware so that it blocks any user interactions.

The best place to return this information would be under the health check endpoint

Start at the health check endpoint and trace how the indexer records or exposes its bootstrap state. Confirm the endpoint reports isBootstrap while bootstrap is running, and verify the response returns to its normal state afterward so the FE can block and resume interactions.

Written by the indexing model from the issue text.