Use secret hash instead of resource version to recreate pods when updating secure settings secrets

[thbkrkr]

Problem: If an external tool updates the -es-secure-settings- Secret resource version without updating the Secret data, the operator restarts the Elasticsearch nodes.

Cause: When using secure settings Secrets, the operator uses the resource version of the Secrets to compute the final hash set on the Elasticsearch pods label in order to recreate Pods when the Secret changes.

cloud-on-k8s/pkg/controller/common/keystore/user_secret.go

Lines 88 to 90 in 86a25bf

	// resource version will be included in pod labels,
	// to recreate pods on any secret change.
	resourceVersion := secret.GetResourceVersion()

Proposal: use a hash of the Secret data instead of the resource version.