[Bug] overlay_dir setting does not resolve ~

[ismay]

Describe the Bug

On linux, the qmk_home setting resolves tildes to the user's home dir. So this:

[user]
qmk_home = ~/code/qmk_firmware

Will resolve the qmk_home to /home/currentuser/code/qmk_firmware. But the overlay_dir setting does not do this, so this:

[user]
qmk_home = ~/code/qmk_firmware
overlay_dir = ~/code/qmk_userspace

will not work. This does work:

[user]
qmk_home = ~/code/qmk_firmware
overlay_dir = /home/currentuser/code/qmk_userspace

But that seems wrong to me. It would be nice if using the tilde to refer to $HOME would be supported for the overlay_dir as well.

Additional Context?

Maybe this should be in the firmware repo instead btw. Feel free to move it there if more appropriate.