[NET-11256] Add gateway list command to consul-k8s CLI

[nathancoleman]

Note

This PR is blocked by the bug fix in #4434 which is preventing tests from passing

Changes proposed in this PR

This PR adds a new command, consul-k8s gateway list, which collects the various components of configuration for all Gateways in a given K8s cluster or namespace – Gateway, attached HTTPRoutes, attached TCPRoutes, etc. – into a single zip file containing one yaml file per Gateway.

It can output an archive named gateways.zip into the current directory, or it can output JSON to the terminal.

# Output a zip archive for all gateways in the current namespace on your kubecontext
$ consul-k8s gateway list --output archive

# Output JSON to the terminal for all gateways in the <my-namespace> namespace
$ consul-k8s gateway list --namespace my-namespace --output json

# Output JSON to the terminal for all gateways in the k8s cluster
$ consul-k8s gateway list --all-namespaces --output json

How I've tested this PR

Create one or more Gateways in your Kube cluster. Example for this config is available here.

Run the commands above to inspect the various forms of output, making sure to use both the implicit namespace on your kubecontext and an explicit --namespace <my-namespace> arg.

How I expect reviewers to test this PR

See above

Checklist

• Tests added
• CHANGELOG entry added

[NiniOak]

Should there be Aliases for this flag?

[nathancoleman]

I made it consistent with the existing consul-k8s proxy list command which doesn't specify an alias. I'm not finding any other commands that specify an alias, so I think it makes sense not to have one here for consistency.

consul-k8s/cli/cmd/proxy/list/command.go

Lines 89 to 94 in acb1af8

	f.StringVar(&flag.StringVar{
	Name: flagNameKubeContext,
	Target: &c.flagKubeContext,
	Default: "",
	Usage: "Set the Kubernetes context to use.",
	})