Add connection_string secret to default_user secret

[hxyannay]

This closes #1722

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

Summary Of Changes

Added a new key connection_string to the default_user secret with a formatted connection_string.

[Zerpet]

Thank you for this contribution. I like this idea. I left some cosmetic suggestions.

[Zerpet]

It is looking better 👍 I left two suggestions before approving this PR.

[hxyannay]

Committed your changes :)
Also it would be great if you could release a new version of the operator once you merge this pull request, so I could use those changes right away.

[hxyannay]

Hey @Zerpet
Can you take another look?
Thanks!

[Zerpet]

I approved the PR ✅ I'll merge after CI passes. We released 2.10.0 last week, and it is a bit soon to release another version. We tend to wait for 1 month between minor releases. Plus we have some dependabot PRs that need manual intervention.

If you want to use these changes right away, I'd recommend that you build own "snapshot" version from main after merging. There's a Make target to build, and it only requires 2 inputs, see:

cluster-operator/Makefile

Lines 207 to 210 in 86e948e

	docker-build: ## Build the docker image with tag `latest`
	@$(call check_defined, OPERATOR_IMAGE, path to the Operator image within the registry e.g. rabbitmq/cluster-operator)
	@$(call check_defined, DOCKER_REGISTRY_SERVER, URL of docker registry containing the Operator image e.g. registry.my-company.com)
	docker buildx build --build-arg=GIT_COMMIT=$(GIT_COMMIT) -t $(DOCKER_REGISTRY_SERVER)/$(OPERATOR_IMAGE):latest .

You can build the operator locally, for example, with:

make docker-build DOCKER_REGISTRY_SERVER=docker.io OPERATOR_IMAGE=hxyannay/rabbitmq-cluster-operator

You will have to push the image then with docker push and update the latest release manifests to use this image.

[hxyannay]

Great, I will build an image myself for the time being.
Thank you.