[8.0] Deprecate ARC and ARC6

[aldbr]

Based on the following discussion: https://github.com/DIRACGrid/DIRAC/discussions/7551

BEGINRELEASENOTES *Resources CHANGE: mark ARC and ARC6 as deprecated ENDRELEASENOTES

[DIRACGridBot]

Sweep summary

Sweep ran in https://github.com/DIRACGrid/DIRAC/actions/runs/9420068098

Failed:

• integration cherry-pick 725cd3a41 into integration failed check merge conflicts on a local copy of this repository

  git fetch upstream
  git checkout upstream/integration -b cherry-pick-2-725cd3a41-integration
  git cherry-pick -x -m 1 725cd3a41
  # Fix the conflicts
  git cherry-pick --continue
  git commit --amend -m 'sweep: #7656 Deprecate ARC and ARC6' --author='aldbr <aldbr@outlook.com>'
  git push -u origin cherry-pick-2-725cd3a41-integration
  
  # If you have the GitHub CLI installed the PR can be made with
  gh pr create \
     --label 'sweep:from rel-v8r0' \
     --base integration \
     --repo DIRACGrid/DIRAC \
     --title '[sweep:integration] Deprecate ARC and ARC6' \
     --body 'Sweep #7656 `Deprecate ARC and ARC6` to `integration`.
  
  Adding original author @aldbr as watcher.
  
  BEGINRELEASENOTES
  *Resources
  CHANGE: mark ARC and ARC6 as deprecated
  ENDRELEASENOTES
  Closes #7659'