Add reusable workflow for build_docs

[mwittgen]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Merging #18 (3fd2144) into main (3683fb8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #18   +/-   ##
=======================================
  Coverage   85.73%   85.73%           
=======================================
  Files          22       22           
  Lines        2726     2726           
  Branches      542      542           
=======================================
  Hits         2337     2337           
  Misses        305      305           
  Partials       84       84           

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