Allow for changing the linux username

[darltrash]

Problem

There should be a way to change the linux username, I don't mean just my actual formal name, but the name as stated by whoami

Proposal

There should be a way of changing the user name, though I believe it'll require a lot of design, since it is not possible to do so while the user is still "online" AFAIK

Prior Art (Optional)

No response

[cyrneko]

Yeah as far as I know, the operations must happen while the user is logged out, from another user (i.e root, a systemd-managed user or else) and then the home must be migrated