(feat) SveltosCluster Readniness and Liveness Checks

[gianlucam76]

Introduce ReadinessChecks and LivenessChecks.

ReadinessChecks are evaluated till SveltosCluster moves to ready. LivenessCheckes are periodically evelauated after that.

This is an example of ReadinessChecks waiting for at least one worker node to exist in the cluster

apiVersion: lib.projectsveltos.io/v1beta1
kind: SveltosCluster
metadata:
  name: staging
  namespace: default
spec:
  consecutiveFailureThreshold: 3
  kubeconfigName: clusterapi-workload-sveltos-kubeconfig
  readinessChecks:
  - condition: |-
      function evaluate()
        hs = {}
        hs.pass = false

        for _, resource in ipairs(resources) do
          if  not (resource.metadata.labels and resource.metadata.labels["node-role.kubernetes.io/control-plane"]) then
            hs.pass = true
          end
        end

        return hs
      end
    name: namespace-bar-check
  resourceSelectors:
  - group: ""
    kind: Node
    version: v1
status:
  connectionStatus: Down
  failureMessage: cluster check namespace-bar-check failed

This PR also makes sure a SveltosCluster instance is reconciled only
on Create, Delete and Update when Spec changes (so Status changes do not
cause a reconciliation)