Upgrade to isolate v2

[wil93]

In order to upgrade to isolate v2 we need to:

• Switch the Github Actions runner from 20.04 to at least 22.04, where ubuntu seems to drop the unsupported "unified cgroups" hierarchy and only provides the new cgroup v2. Probably it makes sense to just go with 24.04 since anyway we only use this to call docker.
• Add cgroup: host to the docker-compose file to run the container in the host's cgroup namespace (docs).
• Currently isolate is installed by prerequisites.py with default settings. In the default settings, isolate expects /run/isolate/cgroup to exist. This normally gets created by isolate-cg-keeper, which is what the isolate.service systemd unit is meant for. If we want users to install and enable that unit, then we should add it to the documentation (and possibly make prerequisites.py install the unit). I'm not sure however if it's really needed to run that, since just running echo /sys/fs/cgroup > /run/isolate/group manually seems to also work. Maybe we can instead configure isolate to always use /sys/fs/cgroup (I think we can do it by changing the default configuration in /usr/local/etc/isolate) and document this instead? We need to figure out which of these approaches are OK, and add it to the documentation.

Fixes #1257

[gollux]

Cgroup v2 support is now present in the latest release of Isolate. See also #1257.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.55%. Comparing base (b77c87b) to head (9a5c27c).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1222      +/-   ##
==========================================
+ Coverage   69.39%   69.55%   +0.15%     
==========================================
  Files         328      328              
  Lines       26201    26201              
==========================================
+ Hits        18182    18223      +41     
+ Misses       8019     7978      -41     

Flag	Coverage Δ
functionaltests	47.22% <100.00%> (+0.47%)	⬆️
unittests	56.80% <0.00%> (+<0.01%)	⬆️

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[CristianCantoro]

To clarify, until this gets merged we should still use the kernel flags as detailed in ioi/isolate#35, correct?

At the moment, using v1.4.rc1, I get the following cgroups-related error:

Failed to create control group /sys/fs/cgroup/memory/box-0/: No such file or directory
Traceback (most recent call last):
  File "/home/cms/cms_venv/bin/cmsMake", line 11, in <module>
    load_entry_point('cms==1.4rc1', 'console_scripts', 'cmsMake')()
  File "/home/cms/cms_venv/lib/python3.6/site-packages/cms-1.4rc1-py3.6.egg/cmstaskenv/cmsMake.py", line 755, in main
    assume=assume)
  File "/home/cms/cms_venv/lib/python3.6/site-packages/cms-1.4rc1-py3.6.egg/cmstaskenv/cmsMake.py", line 692, in execute_multiple_targets
    already_executed, debug=debug, assume=assume)
  File "/home/cms/cms_venv/lib/python3.6/site-packages/cms-1.4rc1-py3.6.egg/cmstaskenv/cmsMake.py", line 682, in execute_target
    action(assume=assume)
  File "/home/cms/cms_venv/lib/python3.6/site-packages/cms-1.4rc1-py3.6.egg/cmstaskenv/cmsMake.py", line 269, in test_src
    assume=assume)
  File "/home/cms/cms_venv/lib/python3.6/site-packages/cms-1.4rc1-py3.6.egg/cmstaskenv/Test.py", line 163, in test_testcases
    tasktype.evaluate(job, file_cacher)
  File "/home/cms/cms_venv/lib/python3.6/site-packages/cms-1.4rc1-py3.6.egg/cms/grading/tasktypes/Batch.py", line 290, in evaluate
    sandbox = create_sandbox(file_cacher, name="evaluate")
  File "/home/cms/cms_venv/lib/python3.6/site-packages/cms-1.4rc1-py3.6.egg/cms/grading/tasktypes/util.py", line 71, in create_sandbox
    sandbox = Sandbox(file_cacher, name=name)
  File "/home/cms/cms_venv/lib/python3.6/site-packages/cms-1.4rc1-py3.6.egg/cms/grading/Sandbox.py", line 944, in __init__
    self.initialize_isolate()
  File "/home/cms/cms_venv/lib/python3.6/site-packages/cms-1.4rc1-py3.6.egg/cms/grading/Sandbox.py", line 1420, in initialize_isolate
    "(error %d)" % (pretty_print_cmdline(init_cmd), ret))
cms.grading.Sandbox.SandboxInterfaceException: Failed to initialize sandbox with command: isolate --cg --box-id=0 --init (error 2)