Add new startup logging to replace Celery's.
Review Request #12098 — Created March 2, 2022 and submitted
When starting a new Review Bot worker process, Review Bot will now log
some information on the configuration. This lists the available tools,
the ones missing dependencies, the ones that require repository
configuration, and the available repositories. URLs for the relevant
sections in the manual are also provided.
This replaces the default Celery startup information, which, while
somewhat interesting, isn't generally useful for Review Bot. We can only
outright replace it with Celery 4+ on Python 3. On Python 2.7, the old
Celery banner will still display.
The logging is now done through a new root logger, which just uses
"Review Bot" as the name, rather than a module path. The configuration
code uses this logger as well, since the logging there ties more into
Ran Review Bot with Python 2.7 and 3.x. Verified the details of the
startup information. Verified that the Celery banner didn't dsiplay
Unit tests pass.