Add PNG optimization to pre-commit

[StanFromIreland]

It might be worth adding a pre-commit check (or workflow?) to check that images are not larger than they need to be when added or changed.

Originally posted by @zware in #138842 (comment)

From some quick research, I see https://github.com/oxipng/oxipng may be a good option.

Linked PRs

• gh-138848: Add PNG optimization pre-commit hook #138849
• gh-138848: Add PNG optimization to pre-commit #139061

[serhiy-storchaka]

Is it supposed to run each time you make a commit in a PR? New PNG files are added once in few years, I don't think it's worth the price.

[StanFromIreland]

On my machine, the check takes 11ms, not a noticeable difference for me.

[zware]

This particular check should only run locally when a matching file is added or changed, though CI will run it always due to using --all-files. We should consider adjusting that to only run on changed files, which would also resolve the issue of CI adjusting the images we don't want to bother with without having to exclude them specifically.