The login name of the authenticated user will be readily available only
if authentication info comes from the config file. With other upcoming
authentication modes (for example, the GITHUB_TOKEN environment
variable), the token is the only piece of information we got, so we
would need to additionally query for the login name.
Since `issue status` and `pr status` are the only commands that need the
name of the authenticated user right now, have those commands explicitly
query for the login name. This results in an additional API query, but
simplifies Context implementation and future authentication approaches.
