[UX] Show a user is a service account in `sky api status`

[Michaelvll]

sky api status -a
ID                                    User           Name                                 Created     Status
yyy-yyy skypilot-team  sky.core.status                    5 mins ago  SUCCEEDED
xxx-xxx  skypilot-team  sky.enabled_clouds                   5 mins ago  SUCCEEDED

Here the user skypilot-team is a SA and we should make it clear that it is a service account, e.g., make it skypilot-team (SA)