debian: Use update-alternatives and release 0.22.0~rc1

This allows for easy selection between squeekboard and phosh-osk-stub while having both packages installed.

Note that the user can still override the OSK completely via usr/share/applications/sm.puri.OSK0.desktop.

This is mostly a downstream thing but will be good to provide this upstream too to avoid conflicts.

Signed-off-by: Guido Günther guido.gunther@puri.sm