Run upstream Argo Rollouts E2E tests on argo-rollouts-manager PRs (#30)

[jgwest]

What does this PR do / why we need it:

• Contributes a shell script which automatically clones argo-rollouts, and runs the E2E tests against the repo
• Adds a new GitHub workflow to run the above script
• Fixes a missing test CR, apisix, which needs to be added for the test to pass

Have you updated the necessary documentation?

• [ ] Documentation update is required by this PR, and has been updated.

Which issue(s) this PR fixes: Fixes #30

How to test changes / Special notes to the reviewer: N/A