[kubetest2-gke deployer] Automatically resolves the release channel if it's not specified

[chizhg]

Sometimes when the users create the GKE clusters, they just want to specify a valid cluster version but do not want to hard code the channel, but if the version is only valid in a specific channel (e.g. rapid), the cluster creation will fail.

This PR adds the support to automatically resolve the release channel if it's not specified, so that as long as the specified version is in any of the valid release channels, kubetest2 gke --up will work.

/cc @amwat

[amwat]

Let's make this best-effort instead of a run failing error.
Otherwise lgtm.

Isn't None channel usually a superset of all channels except maybe Rapid?

[amwat]

maybe can reuse toReleaseChannel to avoid needing sets.

[chizhg]

toReleaseChannel is used to convert the channel name in the server config to the channel name in the gcloud flag, so it cannot be used here. I have changed to simple array iteration to avoid using sets.

[amwat]

I meant since the strings are the same, we can use toLower/toUpper and the default case to also use it as a validation method.
But considering it's just 4 values the array solution is fine as well.

[amwat]

/lgtm
/approve

/hold

couple of nits feel free to cancel the hold.

[amwat]

nit:

also add a case with version and target swapped to exercise

if len(parts) < len(matchParts) {
		return false
	}

[chizhg]

👍 I'll address this comment in my next PR.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: amwat, chizhg

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[chizhg]

/unhold