RFE: Add a hidden option to ostree admin kargs edit-in-place to update all existing deployments in place

[HuijingHei]

Describe the enhancement

Add a hidden option to ostree admin kargs edit-in-place to update all existing deployments in place.

Example:

$ sudo ostree admin kargs edit-in-place --append-if-missing=rw
This would be useful for: https://fedoraproject.org/wiki/Changes/Silverblue_Kinoite_readonly_sysroot

[cgwalters]

My main uncertainty here is whether this is a new subcommand or simply a flag. The current proposal is a subcommand, but I think a flag makes more sense because it can apply to all other operations (delete/add) etc.

In the subcommand version:

$ ostree admin kargs edit-in-place --append=foo=bar`
$ ostree admin kargs --append=foo=bar

In the flag version:

$ ostree admin kargs --in-place --append=foo=bar
$ ostree admin kargs --append=foo=bar

[lucab]

@cgwalters we'd like to scope this logic into an hidden subcommand, solving the immediate needs of Silverblue only. This task has two odd semantic requirements (in-place changes; tweaking all the deployments) which we'd like not to advertise too much.

For future public kargs verbs we'd like to stick to something similar to rpm-ostree behavior, which creates new deployments and does not touch inactive ones. In that regard, future non-hidden/documented subcommands may look like this:

$ sudo ostree admin kargs edit --append-if-missing=rw
## Creates new deployment, starts from the default active one, does not impact inactive ones

$ ostree admin kargs editor
## Like the one above, but interactive editing via $EDITOR

Flags like --in-place and --all-deployments will create odd mixes, which we'd like not to surface to users right now as we hope to keep future UX cleaner and closer to the existing rpm-ostree one.

[HuijingHei]

Both make sense, the flag version can better reuse the code, and subcommand version make the logic more specific.
I will try with subcommand version (like sudo ostree admin kargs edit-in-place --append-if-missing=rw), when review if found the other is better then can change

@travier @cgwalters @lucab @jlebon , WDYT?

[cgwalters]

I will try with subcommand version (like sudo ostree admin kargs edit-in-place --append-if-missing=rw), when review if found the other is better then can change

Sounds good to me!

[HuijingHei]

Close this refer to #2639