Summary:
The flag is used both by the sender in remote_bootstrap_session and the receiver in
remote_bootstrap_file_downloader and is updated on new sessions / new file downloads, respectively.
Jira: DB-18294

Test Plan: existing tests

Reviewers: bkolagani

Reviewed By: bkolagani

Subscribers: ybase

Differential Revision: https://phorge.dev.yugabyte.com/D46782