docs: Move to sphinx-autoissues

[tony]

https://github.com/tony/sphinx-autoissues (Homepage)

This is a fork of sphinxcontrib-issuetracker but heavily modified. In the end the similarities between the packages may be less: But the major point is we want plain text issues to be linked

[codecov]

Codecov Report

Merging #378 (579dcf3) into master (f9278bb) will not change coverage.
The diff coverage is n/a.

❗ Current head 579dcf3 differs from pull request most recent head 77f0586. Consider uploading reports for the commit 77f0586 to get more accurate results

@@           Coverage Diff           @@
##           master     #378   +/-   ##
=======================================
  Coverage   87.40%   87.40%           
=======================================
  Files          13       13           
  Lines         675      675           
=======================================
  Hits          590      590           
  Misses         85       85           

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