Implement dynamic middle panes for EU Galaxy servers

[NickSto]

This is basically a subset of #1380, but I'm making a separate issue because the dynamic pages are a special effort. Here we can have a checklist for each individual page, and close it when they're all done.

	Server	.eu page	.org page
✔	usegalaxy.eu	galaxy/index.md	content/bare/eu/usegalaxy/main/index.md
✔	metabolomics.usegalaxy.eu	index-metabolomics.md	content/bare/eu/usegalaxy/metabolomics/index.md
✔	proteomics.usegalaxy.eu	index-proteomics.md	content/bare/eu/usegalaxy/proteomics/index.md
✔	?	freiburg/galaxy/index.md	content/bare/eu/usegalaxy/freiburg/index.md
✔	erasmusmc.usegalaxy.eu	erasmusmc/galaxy/index.md	content/bare/eu/usegalaxy/erasmusmc/index.md
✔	usegalaxy.be	belgium/galaxy/index.md	content/bare/eu/usegalaxy/belgium/index.md
✔	galaxy.pasteur.fr	pasteur/galaxy/index.md	content/bare/eu/usegalaxy/pasteur/index.md
✔	galaxy.genouest.org	genouest/galaxy/index.md	content/bare/eu/usegalaxy/genouest/index.md
✔	usegalaxy.fr	ifb/galaxy/index.md	content/bare/eu/usegalaxy/ifb/index.md

[NickSto]

Done as of #1573