Add issue-manager

[foarsitter]

Automatically close issues or Pull Requests that have a label, after a custom delay, if no one replies back.

This PR adds https://github.com/tiangolo/issue-manager to the github workflows. The config is borrowed from cookiecutter-django.

It will help closing issues and PR's without any wrongdoing against the original poster.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.57%. Comparing base (6e7158b) to head (c380b3b).
Report is 20 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #600   +/-   ##
=======================================
  Coverage   98.56%   98.57%           
=======================================
  Files           6        6           
  Lines         768      773    +5     
=======================================
+ Hits          757      762    +5     
  Misses         11       11           

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