Improve doc install pages

[jessica-mitchell]

This PR builds on #3066 focusing on the install pages, to make it easier to access the various methods we have for installation, the index page is updated with links and nestml and nest-desktop are clearly marked as well as projects to look at as well. It cannot be merged until #3066 so will be labeled blocked

[jessica-mitchell]

@ddahmen @heplesser @steffengraber @clinssen

output here

Changes made

• [x] removed HPC card and instructions
• [x] moved minimal configuration to cmake options
• [x] Add EBRAINS install free in separate PR

TODO

improve HPC install instructions

[jessica-mitchell]

Actually, I noticed that in the #3066 version, we have page https://nest-simulator--3066.org.readthedocs.build/en/3066/installation/admin.html#admin-install. On it, the link under "Configure HPC Systems" leads to a page without useful information, but the other links, namely

* https://nest-simulator--3066.org.readthedocs.build/en/3066/hpc/optimizing_nest.html#optimize-performance

* links to docker instructions
  provide useful information. It would be good if we could keep links to them from the install page.

So the docker instructions are already on the install page, but I added a card about configuring HPC systems there

[jessica-mitchell]

@jessica-mitchell Would you mind moving the "Configure HPC" card to the top row? It looks rather strange with the open space on the top right.

This will be fixed in the PR that adds the EBRAINS card #3121

[heplesser]

@jessica-mitchell Would you mind moving the "Configure HPC" card to the top row? It looks rather strange with the open space on the top right.

This will be fixed in the PR that adds the EBRAINS card #3121

Good!

[clinssen]

@jessica-mitchell Would you mind moving the "Configure HPC" card to the top row? It looks rather strange with the open space on the top right.

This will be fixed in the PR that adds the EBRAINS card #3121

Good!

It has disappeared entirely in that PR, is that the intention?