prevent non-superuser terminate bgworker running as superuser

Hi All,

Currently, BackgroundWorker connected to a database by calling
BackgroundWorkerInitializeConnection with username as NULL can be
terminated by non-superuser with pg_signal_backend privilege. When the
username is NULL the bgworker process runs as superuser (which is
expected as per the documentation -
https://www.postgresql.org/docs/current/bgworker.html ), but can the
non-superuser (with pg_signal_backend) terminate this superuser owned
process?
We (Mahendrakar and Myself) think that this is a bug and proposing a
fix that sets MyProc->roleId to BOOTSTRAP_SUPERUSERID, similar to
InitializeSessionUserId, to prevent non-superuser terminating it.

Please let us know your comments.

Thanks,
Hemanth Sandrana