Add migration spec for kernel -> kernel-clk6.12 namespace transition

[bmastbergen]

The namespaced kernel packages (kernel-clk6.12-*) carry Provides and Conflicts for their non-namespaced equivalents, which prevents co-installation but doesn't create an automatic upgrade path. DNF's dnf upgrade only considers packages with the same name as what's already installed, so it won't spontaneously replace kernel-headers with kernel-clk6.12-headers just because the latter provides and conflicts with the former. Even adding Obsoletes to the namespaced packages wouldn't help, since DNF doesn't evaluate Obsoletes from packages it isn't already considering for installation. The migration package solves this as a one-time explicit action: dnf install kernel-clk6.12-migrate. It uses rich deps to detect which old non-namespaced packages the user has installed, pulls in shim subpackages that Obsoletes those specific old versions, and Requires the namespaced replacements. A systemd oneshot service then cleans up old installonly packages (kernel-core, kernel-modules) on the next reboot, since those can't be removed mid-transaction when they belong to the running kernel.

This may not be the best place for this spec to live, but I've put it here so at least we can have a PR to discuss the issue in.

[jdieter]

I think this is the wrong approach. Instead of using requires and scriptlets to remove the old packages, we should have

Provides: subpackage-name = %{some version}
Obsoletes: subpackage-name < %{some_version}
Requires: kernel-clk6.12-subpackage-name

This should remove the requirement for the boolean dependencies and for users to manually install the migration package. With the above, a simple dnf update should automatically transition users from the old non-namespaced CLK kernels to the new namespaced ones. Note that it will also transition stock Rocky kernels to the new CLK kernels, which is why it should only live in the current CLK repo.