mgr/dashboard: Optimize RBD list request on iSCSI form
iSCSI form is taking too long to open due to a request to the RBD images list that is then used to populate the "Images" dropdown:
This request is returning a lot of information that is not needed in this form (e.g. disk usage):
We should only request the required RBD image fields in order to optimize the initial load of this form.