conformance test cleanup

[jenshu]

Clean up the conformance tests to mirror the changes made in https://github.com/solo-io/solo-projects/pull/6065

• defined a composite action, that is used by both PR and nightly regression tests
• moved make targets and kind setup into the main Makefile and setup-kind.sh
• removed conformance_test.go from git because that is pulled in dynamically BOT NOTES: resolves https://github.com/solo-io/solo-projects/issues/5751

[solo-changelog-bot[bot]]

Issues linked to changelog: https://github.com/solo-io/solo-projects/issues/5751

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 92a33e3):

https://gloo-edge--pr9407-conformance-test-cle-yz8755u9.web.app

_{(expires Mon, 06 May 2024 16:13:46 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}

_{Sign: 77c2b86e287749579b7ff9cadb81e099042ef677}

[stevenctl]

Seems like this and probably some other changes broke existing scripts like gateway2/install.sh