Consider adding PID file for communicating with UWSGI process

[paulmueller]

UWSG supports sending signals to an existing process: https://uwsgi-docs.readthedocs.io/en/latest/Management.html

To support this, one would only need to set/add the --safe-pidfile /tmp/uwsgi.pid option.

Then, UWSGI can be told to reload using uwsgi --reload /tmp/uwsgi.pid

Background: I am modifying the CKAN installation heavily via plugins and would like to ensure UWSGI picks up those changes. My tests run through on GitHub Actions, but the current situation (Modifying CKAN installation via steps in GHA yaml after UWSGI started) seems not very clean.

(I can create the PR if this is accepted)

[wardi]

This is a great idea. It would also simplify development scripts like https://github.com/ckan/ckan-docker/blob/master/bin/reload