bootc: Implement the 'remove' subcommand

[dcantrell]

Implement the 'remove' subcommand for the bootc plugin and add documentation. Most of the options for this subcommand will come from global dnf command line option settings. The only option not handled is --os=OSNAME from rpm-ostree.

https://issues.redhat.com/browse/SWM-3098

[evan-goode]

Oh, I thought we were not going to implement install and remove via rpm-ostree since these will break bootc upgrade: https://docs.fedoraproject.org/en-US/bootc/rpm-ostree/#_rpm_ostree_installoverride_replace. But I suppose we will decide that on Monday's meeting with the bootc people.

IMO the plan for now should be to have the dnf4 bootc install and remove commands support --transient only and call rpm-ostree usroverlay and then set up an ordinary DNF transaction.