Values:
STAGE_UNSPECIFIED (0):
No stage specified.
PENDING_CREATE_APP (1):
Only for GitHub Enterprise. An App creation
has been requested. The user needs to confirm
the creation in their GitHub enterprise host.
PENDING_USER_OAUTH (2):
User needs to authorize the GitHub (or
Enterprise) App via OAuth.
PENDING_INSTALL_APP (3):
User needs to follow the link to install the
GitHub (or Enterprise) App.
COMPLETE (10):
Installation process has been completed.