Add ability to remove the user lock file to release updates

[mirkobrombin]

Currently, if the user interrupt an upgrade from the vso-gnome-ext, it is not possible to remove it if not manually from /tmp. We need a command to simplify the process, for example abroot remove-user-lock or abroot unlock-updates in we also want to remove the internal upgrade lock file, in case it was kept, in this last case we should also check if an abroot process is running, to avoid breaking updates.

[axtloss]

I dont think users should be able to remove lockfiles
We instead should be putting more effort into ensuring that the lockfile gets properly removed by abroot when the user cancels an upgrade

[mirkobrombin]

I was thinking about it, but I think the "user" lock should stay for the entire session. I mean, updates are done at intervals while the smaller one is "daily", so it might only be an issue for those who don't turn off their device in 1 day.

[taukakao]

I think we should have both a file that locks abroot during an upgrade and a file that locks it after an upgrade completed successfully.

So if an upgrade fails, then the first lock file will be removed but the second lock file will not be created.