Block installation of Elastic Stack if cluster does not have enough resources

Ensure your cluster contains at least three nodes of instance types larger than f1-micro, g1-small, or n1-standard-1.

Please see https://docs.gitlab.com/ee/user/clusters/applications.html#elastic-stack for more requirements.

In #273449 (closed), the installation errors out with an unclear message:

[kube] 2020/10/28 17:44:17 Pod is not ready: gitlab-managed-apps/elastic-stack-filebeat-rvdx4
[tiller] 2020/10/28 17:44:17 failed install perform step: release elastic-stack failed: timed out waiting for the condition

Proposal

Consider blocking installation if the cluster does not have the required resources.