build: Revise MANIFEST.in strategy to properly use prune

[matthewfeickert]

Resolves #73

Copy of scikit-hep/pyhf#1449

* Remove global exclude of dotfiles from MANIFEST.in to avoid potential problems with build systems
   - c.f. https://github.com/scikit-build/scikit-build/issues/537
* Use `prune **` to remove all files from the sdist
   - c.f. https://packaging.python.org/guides/using-manifest-in/#manifest-in-commands
   - "Setuptools also has undocumented support for ** matching zero or more characters including forward slash, backslash, and colon."
* Manually include all "default" files for a sdist in MANIFEST.in
   - c.f. https://packaging.python.org/guides/using-manifest-in/#how-files-are-included-in-an-sdist
* Add list of sdist contents to package publishing CI
   - Allow for easier checking of the sdist contents in CI logs

[codecov]

Codecov Report

Merging #75 (6ac30ea) into main (ec5b039) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #75   +/-   ##
=======================================
  Coverage   25.21%   25.21%           
=======================================
  Files           7        7           
  Lines         238      238           
  Branches       38       38           
=======================================
  Hits           60       60           
  Misses        178      178           

Flag	Coverage Δ
unittests	25.21% <ø> (ø)

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