Add a CLI option to not auto apply every image

[carol-apple]

Problem

With #16482, a real Linux image is needed because it will apply the downloaded image via an execv. Prior to this change, it was a noop when an "apply" occurred so any small file can be used to test OTA transfer succeeded.

Without a proper image, the ota-requestor-app would terminate after the image has been transferred because it would be automatically applied.

A real Linux image is > 5.6 MB. This would take a significant amount of time to test a basic transfer flow.

Proposed Solution

Add a CLI option to make applying optional so that testing/development can continue without either of the two current outcomes above.