plots: support svg

[blakeNaccarato]

Add SVG to parser and parametrize an existing functionality test on SVG as well as JPG.

If needed I can also modify a test in tests/integration/plots to check SVG functionality. I haven't done that yet as it would touch quite a few lines.

Fixes #6714.

• ❗ I have followed the Contributing to DVC checklist.

• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here.

^ Regarding the documentation check above, I will add SVG to the list under plots over in the documentation as needed.

[codecov]

Codecov Report

Base: 94.30% // Head: 94.30% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (560be12) compared to base (a6bfc7d).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8542   +/-   ##
=======================================
  Coverage   94.30%   94.30%           
=======================================
  Files         429      429           
  Lines       32822    32825    +3     
  Branches     4591     4592    +1     
=======================================
+ Hits        30954    30957    +3     
  Misses       1450     1450           
  Partials      418      418           

Impacted Files	Coverage Δ
tests/func/plots/test_show.py	100.00% <100.00%> (ø)

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[pared]

Image files are pasted into <img> section, so I think we don't necessarily need a specific integration test for that.

[blakeNaccarato]

Thanks! I've opened an issue (treeverse/dvc.org#4109) over at https://github.com/iterative/dvc.org to track my related documentation.

I hope that the broken CI after merging to main is due to it just being the first merge after the PR that added the all-OS Python 3.11 tests.