Used to retrieve the current user name. Will request the username be entered
if no user is provided and `interactive()` is TRUE.
This is largely an internal function, but is exported for awareness and
use in automated pipelines.
Usage
get_username(username = NULL)
Arguments
- username
character if NULL, will be retrieved from the `sb_user`
environment variable or the `username` file stored at `token_stache_path()`
Value
character string containing a username. Throws an error if no
username is found and `interactive()` is FALSE