Migrating Concourse CI pipelines to GH Actions

[coro]

This closes #1202

Note to reviewers: remember to look at the commits in this PR and consider if they can be squashed

Summary Of Changes

• Move the cluster operator to be a multiarch OCI built on AMD64 and ARM64, instead of just the former.
• Move existing Concourse CI infrastructure to GitHub Actions

Additional Context

The pipeline now runs, on PRs:

• kubectl tests
• Unit tests
• Integration tests
• Tests that a multiarch OCI can be successfully built, but does not push it
• Runs system tests locally against kind, for multiple RabbitMQ Cluster versions
  • This excludes the volume expansion system tests
• Runs the documented examples against kind in 'dry-run' mode

On pushes to main:

• kubectl tests
• Unit tests
• Integration tests
• Builds a multiarch OCI of the operator (pushed to rabbitmqoperator/cluster-operator with a tag of the SHA256 and edge), and a manifest referencing that OCI
• Also builds a single-arch version of the image, for AMD64, for compatibility with internal tooling
• Runs system tests against GKE, for multiple RabbitMQ Cluster versions
• Runs the documented examples against GKE
• Tests if upgrading to the operator built earlier would cause a rolling restart of RabbitmqClusters

On creation of a tag in the repo:

• Same as push to main, except in addition:
  • OCI is tagged also with latest if the latest version, and the semver version of the release
  • Uploads manifests to a release in GitHub as a Draft release

N.B.: This PR removes the use of the rabbitmqoperator/cluster-operator-dev image, as it's now functionally replaced by the regular image with a SHA tag.

Local Testing

Please ensure you run the unit, integration and system tests before approving the PR.

To run the unit and integration tests:

$ make unit-tests integration-tests

You will need to target a k8s cluster and have the operator deployed for running the system tests.

For example, for a Kubernetes context named dev-bunny:

$ kubectx dev-bunny
$ make destroy deploy-dev
# wait for operator to be deployed
$ make system-tests

[ablease]

Based upon sequential changes to the same file you could squash the following sets of commits.

Makefile changes: [c8aa3a1 b490b8c]
Build-Test-Publish changes: [30e571b eb3ef54 8806354 6395e01 5b60d84 05c2ec9 037c46c 2338cdd]

Makefile Changes Round 2: [afb8bf2 1201371]

Build-test-publish Round 2 [e750037 e7b1016]

Build-test-publish Round 3 [dbef9a3 70a9428]

Build-test-publish Final Round! [40ab6c1 f06842d]

I can't say to much about the github actions changes themselves, will keep an eye on them as they run :) Thanks!

[ChunyiLyu]

Some minor comments. Looks good!

[ChunyiLyu]

Why 1.12.0 as the baseline version? Do we plan to bump this version with new minors released in the future?

[coro]

The baseline is the most recent release that contained a change that caused a rolling restart. We discussed the possibility of limiting these changes to only major version updates instead, but for now this replicates the behaviour of the hush house CI.