Modify kernel parameters

[matbme]

This PR adds support for modifying kernel parameters with abroot kargs edit, similarly to what was present in v1.

There is, however, some things still left to resolve:

• For some reason, /etc/abroot/kargs and /etc/abroot/kargs.bak don't get synced if they already exist in the future root, maybe something related to the syncEtc() method.
• ABroot runs a transaction immediately after changing kargs, it's probably a good idea to prompt the user if they want to commit changes now or later (in case they still want to add/remove packages)
• ABroot runs the transaction regardless of whether the user actually changed any kernel parameters or even saved the file. This should be changed.

For now, I'm marking this as a draft.

[mirkobrombin]

What's the status on this?

[matbme]

I couldn't figure out why /etc/abroot/kargs doesn't sync with the rest of the system. Hopefully integrating EtcBuilder into ABRoot will fix the issue and we can merge this.