Make /etc a subvolume that needs no mounting

[NeroReflex]

This is meant to solve the /etc mounting issue where the /etc overlay fires off some race conditions with the system loading resulting in the infamous "gamer is not the password".

This also deals with the overlays that prevents chimeraos team to effectively distribute updates that needs /etc changes.

[alkazar]

Is this necessary? Do we have a mchine-id in our system image such that this would get overwritten? If we do, we should remove it.

[NeroReflex]

This PR, as the hibernation one, was superceeded by the upcoming frzr rework. Machine-id file is created at first boot by systemd on the first boot. I don't know if we have one in our image, but for sure it is something to investigate.

However I don't think we have one simply because systemd is not run from arch-chroot.

Moreover after a system restore the macchine changes id and SSH complains, so I think this is an indirect proof that wedon't ship such a file.

[alkazar]

This introduces complexity which I am not comfortable with.

"Distributing updates to /etc" which will overwrite user's configuration is not something I think we need or should do.
For example, this would revert the password if the user has changed it.

I would much prefer to keep the overlay system we have now. If there is an issue with it, we should try to fix that.

[NeroReflex]

This introduces complexity which I am not comfortable with.

"Distributing updates to /etc" which will overwrite user's configuration is not something I think we need or should do. For example, this would revert the password if the user has changed it.

I would much prefer to keep the overlay system we have now. If there is an issue with it, we should try to fix that.

The problem is articulated in two points, and 3 solutions exists.

1. (Current) user modifications take precedence and we cannot update certain parts of the system. The user requires modifing /etc only once at the risk of (very difficult to spot) incompatibilities
2. (Proposed) updates takes precedence. The user requires constantly editing /etc but this means that everything can be updated, restoring is much easier thanks to snapshots, and since modifications must be replaied it's much easier to spot subtle incompatibilities. This is the solution with higher coherence between the /etc and the rest of the system.
3. 3-way merge that fedora and in general ostree distro uses (and I think bootc too). Difficult to implement and introduces failure point during the upgrade as well as possible incoherent files.

In the case of 2 we can carry over the password as well as machine-id