Improve resource limits and apply only cluster server

Description of changes

• Per-user limits were broken and not being applied. This MR fixes them.
• Removes the awful CPUQuota that makes borg grind to a halt context.
• Changes CPU/IOWeight to more conservative values, in the sense that they are not as extreme changes as before: user's CPU/IOWeight was set to 90 (was 50, default is 100), and the root CPU/IOWeight to 110 (was 200, default is 100).
• Moves the (very restrictive) per-user limits to the cluster server profile
  • By being in the ist-shell profile, they would be applied to labs machines, which is undesirable (local users should freely access memory, cluster users have separate limits set up, SSH users are currently under the same limits as local users but this should be changed in the future).
  • This change leaves nexus out of the per-user limits, but I don't recall an event where a user prevented others from working by using a lot of memory, so it should be fine, at least for now.

Things done

• [-] Tested
  • Last two commits were tested live in borg (it was that bad).
• Updated documentation (Wiki/NetBox)
• Breaking change