Use either "Update" or "Upgrade" consistently in Clusters -> Managed Apps

The problem

The UI to manage K8 apps use the "Upgrade" and "Update" words interchangeably:

The front-end code also presents the same inconsistencies regarding naming:

upgradeButtonLabel() {
  let label;
  if (this.upgradeAvailable && !this.upgradeFailed && !this.isUpgrading) {
    label = s__('ClusterIntegration|Upgrade');
  } else if (this.isUpgrading) {
    label = s__('ClusterIntegration|Updating');
  } else if (this.upgradeFailed) {
    label = s__('ClusterIntegration|Retry update');
  }

  return label;
},
isUpgrading() {
  // Since upgrading is handled asynchronously on the backend we need this check to prevent any delay on the frontend
  return (
    this.status === APPLICATION_STATUS.UPDATING ||
    (this.upgradeRequested && !this.upgradeSuccessful)
  );
},

https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/assets/javascripts/clusters/components/application_row.vue#L212

The proposed solution

I propose to use a single term across the UI. This will bring consistency both from the UX and code maintenance perspectives. Update is more transferable to both situations, so we would use this in all instances.