Address leaking of older kdump initrds that can potentially fill up /boot

[christopherco]

Is your feature request related to a problem? Please describe.
With the introduction of #6479 , if the user enrolls in the new compressed kdump collection option (via force_no_rebuild=0 and mariner_2_initrd_use_suffix=1 in Mariner 2.0, or with default usage in 3.0), we are "leaking" kdump initrds created for older kernels.

We elected not to fix this behavior in our 'stable' release due to risk of regression from hacks to address this. So this feature request is to implement a method to clean up the "leaked" kdump initrds appropriately in our upcoming Azure Linux major release.

See discussion comments:

• fix: introduce mariner_2_initrd_use_suffix kdump.conf option #6479 (comment)
• fix: introduce mariner_2_initrd_use_suffix kdump.conf option #6479 (review)