Use "update" instead of "upgrade" in Clusters -> Managed Apps

In the clusters managed applications app, the words "Upgrade" and "Update" are used interchangeably as if they had the same meaning. This reflects poorly in the code and the user experience as explained in #60852 (closed). The concept of "updating" an application, relates to the action of bumping a Kubernetes application to a newer version. The API uses the term "update/updating/updated" to indicate the current status of the update process. This MR brings consistency by also using "update" in the client.

Closes #60852 (closed)