Initially stemming from BZ #2393662 and a follow-up internal discussion, we should introduce a way to retain arbitrary kernel command line options also in the bootloader configuration of the installed system (with exception of ones that are only consumed by Anaconda, i. e. inst.* and possibly some others).

Currently we can only specify the boot options explicitly in kickstart installation via bootloader --append=, but this rules out manual installations and may add some unnecessary overhead even with kickstart installations, and thus somewhat worsen the UX.

From the user perspective, this functionality should be likely achieved by introducing a new kernel command line option, e. g. inst.preservebootopts, unless there's some better way to achieve the same result.