configure_system: Contrain profile usernames to 32 characters

Previously, we would let a user enter an unbounded name and then
silently truncate away characters that went over the 32-character limit.
This is kind of bad from the UX point of view, because we're essentially
not doing what the user intended in certain scenarios.

Instead, we clamp it to 32 characters and make that visually apparent in
the dialog box to provide a name for a user.