Add username to ProcessConfig proto

[zaporter-work]

See comments here: viamrobotics/docs#3649

Looks like username was never actually added to the protos -- so it doesn't work in the UI.

I'm not sure if you ever expected this to be used in the UI.

@abe-winter We have a few options from here:

• Don't document username (not sure if it was ever supposed to be used from the app config)
• Add username to the protos (Are you hesitant about adding to protos?)

[abe-winter]

lgtm

for clarity -- this only works with processes, not with modules? (or do modules already have a way to do it?)

[zaporter-work]

@abe-winter This would only add it to processes -- not modules. Modules have no way to set a username and it would probably take a lot more work to add to modules.

[zaporter-work]

Oops -- forgot to add @cheukt for code-owner approval.