Provide more UI guidance when creating repositories
Summary: Ref T10923. Walk users through the "create, configure, activate" workflow a little better and set expectations more clearly.
Test Plan:
- Created a new repository, saw new UI help.
- Activated repository, saw onboarding help disappear.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T10923
Differential Revision: https://secure.phabricator.com/D15875