Typically the `LOGNAME` environment variable should be set according
to the values within `/etc/passwd` and represents the name of the
logged in user. This should be set, where possible, alongside the
USER and HOME variables for all drivers that use the shared
executor and do not use a sub-shell.
This PR adds support for the raw_exec driver on systems with only cgroups v2.
The raw exec driver is able to use cgroups to manage processes. This happens
only on Linux, when exec_driver is enabled, and the no_cgroups option is not
set. The driver uses the freezer controller to freeze processes of a task,
issue a sigkill, then unfreeze. Previously the implementation assumed cgroups
v1, and now it also supports cgroups v2.
There is a bit of refactoring in this PR, but the fundamental design remains
the same.
Closes#12351#12348
