Add Custom Image Support for InstaScale in the CodeFlare Operator

[jbusche]

The ability to update or revert the InstaScale image in the InstaScale CR will be very helpful going forward.

[anishasthana]

We would want to update the operator, api, and crd: https://github.com/project-codeflare/codeflare-operator/blob/main/api/v1alpha1/instascale_types.go