Add UI test specs for identity form
We have no UI (Capybara) test coverage for the admin identities form:
- Haml view file:
app/views/admin/identities/_form.html.haml
- EE-only partial:
ee/app/views/admin/identities/_provider_id.html.haml
- EE-only portion:
ee/app/assets/javascripts/pages/admin/identities/ee_toggle_provider_id.js