The need to specify the OCI image is only necessary when deploying local charms. Charms from the store will include the image definition as a resource which is attached to the charm when uploaded to the store and the charm is published.
Juju resources don’t support default values. If the resource type were a zip file instead of an OCI image, you would still need to specify the resource value when deploying a local copy of the charm.
I suggest using a bundle which does support specifying all resources to be associated with a deployed charm. You can add your preferred image path in there.