Implement E2E test framework for testing ApplicationSet against live Kubernetes/Argo CD instance (#65)

[jgwest]

See parent issue for details: #65

To run locally:

• In the PR I've included docs on how to run them (outside the GitHub action), see here: https://github.com/jgwest/applicationset/blob/test-e2e/docs/E2E-Tests.md

[amitkrout]

@jgwest Can you please share the steps for how to verify it, thanks.

[jgwest]

@amitkrout Good thinking, I have documented how to do that as a new markdown file in the PR, you can see it here: https://github.com/jgwest/applicationset/blob/test-e2e/docs/E2E-Tests.md

[wtam2018]

There is significant amount of copied codes from argocd test/e2e. Is there a way to shared these codes?

[jgwest]

@wtam2018 Only <200 lines of code is shared (part of fixture.go, errors.go, cmd.go), I don't think its worthwhile to share them at this time.