New GitHub workflow to generate PR's which update the UML diagrams

[drbenvincent]

• Closes Automate UML image generation #178
• Copied from the approach taken by @wd60622 in pymc-marketing
• Should create PR's on a regular cadence, but only if there are updates to the generated UML diagrams

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📚 Documentation preview 📚: https://causalpy--442.org.readthedocs.build/en/442/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.40%. Comparing base (c0ea8a5) to head (df0c0f9).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #442   +/-   ##
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  Coverage   94.40%   94.40%           
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  Files          31       31           
  Lines        1985     1985           
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  Hits         1874     1874           
  Misses        111      111           

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[wd60622]

Just change these links

[wd60622]

With those changes, it will be good to merge then try out with the workflow_dispatch