Change default behavior for what images are being considered for update

[jannfis]

Is your feature request related to a problem? Please describe.

By default, Argo CD Image Updater ignores images specified in image-list but are not currently deployed with the Application. E.g. it checks whether an image specified in the image-list is actually deployed with the application by inspecting the .status.images field of the Application spec. If this image is not found to be running, Image Updater will skip update with the image xxx does not seem to be live in this application message.

This was an early assumption we made, which proved to be incorrect for a majority of users. More and more people use Image Updater in a way to replace images set in the manifests with custom images. As a workaround, the force-update toggle was introduced which circumvents the liveness check.

Describe the solution you'd like

• The default behavior of Image Updater should be changed to go for trying to update images specified in the image-list, regardless of whether they are currently being deployed with the Application.
• The force-update toggle should be deprecated
• A new toggle (e.g. strict-update: true|false) that reverts the logic of force-update should be introduced. If this is set to true (with a default to false), only live images will be considered for update.