Update Installation Documentation & Matrix

[RasmusOrsoe]

This PR updates the installation doc page in the following ways:

• a new row called "GraphNeT" is added in the installation matrix, so users can choose between different versions of GraphNeT, as opposed to just installing the latest version. Following this PR, users can choose between "v1.8.0 (Stable)" (the default) or "Latest" which is the live main branch. (See attached figure)
• Added documentation for Docker/Apptainer images
• Changed IceTray+GraphNeT installation procedure to recommend our new Apptainer environments
• Minor textual fixes to the km3net part @giogiopg
• Slight reorganization of the page to improve readability.

closes #833 and resolves #741

Snapshot of new installation matrix:

[Aske-Rosted]

Shouldn't we still provide an explanation of how to install into an cvmfs environment?

The way i understand it, the Docker image provides an easy, reproducible way to run GraphNeT as-is. However, if you want to use git and actively develop GraphNeT without losing your changes when the container exits, you need to bind-mount a GraphNeT repository from your host into the container, overriding the copy that was baked into the image.

[giogiopg]

I am okay with every change that have been made and I think the instructions look cleaner now. Apologies for the KM3NeT related mistakes. I have no further comments with respect to deleting the cvmfs related instruction, as I am not familiarized with that installation. With respect to how to run the docker images just one naive question/comment. Will the instructions change a lot if instead of using apptainer singularity was used? Should those instructions be included or rather don'tmake too long this document? I approve the PR as I believe this is up for debate and can be done in future PRs. I consider this PR ready.