Add PNG optimization to pre-commit #138848

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