[4.2.x] Ref #697 - Add traceback logging on SIGUSR1 (backport #721)

[mergify]

This is an automatic backport of pull request #721 done by Mergify.
Cherry-pick of 466849a has failed:

On branch mergify/bp/stable/4.2.x/pr-721
Your branch is up to date with 'origin/stable/4.2.x'.

You are currently cherry-picking commit 466849a.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   docs/admins/deployment.rst
	modified:   irrd/daemon/main.py
	modified:   irrd/utils/process_support.py

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   docs/releases/4.3.0.rst
	both modified:   irrd/server/http/app.py

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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