Update Stratum 1 requirements for disk space

[Neves-P]

No longer recommend a fixed storage amount as a minimum requirement for an S1 server and add link for current usage.

[casparvl]

I think we need some follow-up docs on the option to do partial mirrors as well - we've seen a fair amount of interest in that in the Dutch Tier 2 community and I assume they are not the only ones eager to save some disk space in this day of expensive hardware.

At the very least, I guess we should have an example of how to do this - I think it can be done with a .spec file or something that lists which things to include. I think an example spec file that shows how to

mirror (only) e.g. 2 architecture targets
exclude all arm targets
inludes only particular EESSI versions
would be worthwhile. But... Let's not delay the current PR with that. Would you be up for making a follow-up PR for this though?

Anyway, I don't think we should hold back the current PR - but maybe you are up for doing a follow-up PR with that @Neves-P ?

[Neves-P]

Agreed, the partial mirrors are definitely a priority to add in the docs! I'm happy to work on that, and I might reach out to Valentin to make sure I'm not missing anything when I have a first draft.