Compress images with oxipng

[hugovk]

Updates python#4036.

Make PNGs ~50% smaller with https://github.com/shssoichiro/oxipng.

❯ l peps/pep-0777/*.png
.rw-r--r-- hugo staff 234 KB Thu Oct 10 13:52:34 2024  appendix-dl-by-installer.png
.rw-r--r-- hugo staff 248 KB Thu Oct 10 13:52:34 2024  appendix-dl-by-pip-version.png

❯ oxipng -o max --strip all peps/pep-0777/*.png
Processing: peps/pep-0777/appendix-dl-by-installer.png
Processing: peps/pep-0777/appendix-dl-by-pip-version.png
128694 bytes (49.25% smaller): peps/pep-0777/appendix-dl-by-pip-version.png
119972 bytes (49.99% smaller): peps/pep-0777/appendix-dl-by-installer.png

❯ l peps/pep-0777/*.png
.rw-r--r-- hugo staff 117 KB Thu Oct 10 13:53:03 2024  appendix-dl-by-installer.png
.rw-r--r-- hugo staff 126 KB Thu Oct 10 13:53:03 2024  appendix-dl-by-pip-version.png

[emmatyping-nv]

Good idea! There were directly output from matplotlib, so pretty un-optimized.