Update public REST API docs instead of design docs
- Revert changes to docs/dev/design/apiv3.rst (design docs)
- Add new Build endpoint fields to docs/user/api/v3.rst (public API docs)
- Document commands, commit_url, docs_url, builder fields
- Update expand parameter to include notifications option
Co-authored-by: ericholscher <25510+ericholscher@users.noreply.github.com>