[FEATURE REQUEST] rpm-ostree support for immutable Fedora-based distros

[ekolis]

Please confirm these before moving forward.

• I have searched for my feature proposal and have not found a work-in-progress/duplicate/resolved/discarded issue.
• This proposal is a completely new feature. If you want to suggest an improvement or an enhancement, please use this template.

Describe the new feature

I'd like to see rpm-ostree added as a supported package manager for immutable Fedora-based distros such as Bazzite. Also, it would be nice if UniGetUI could detect that it's running on such a distro and automatically disable the dnf package manager and warn the user that changes made via this package manager will be ineffective since the OS is immutable.

Describe how this new feature could help users

Further unify package management on more operating systems