[ODSC-68321] Create grouped model with multiple verified models

[VipulMascarenhas]

Description

This PR adds the functionality to support group model creation when more than one model is selected to be deployed. The PR does not cover the deployment part, that needs to be covered by a separate PR.

Usage

The create model API is not accessible directly to the user, we need to use the create deployment API to test this.

ads aqua deployment create 
--instance_shape VM.GPU.A10.2 
--display_name "Model grouping deployment"  
--model_info '[{"model_id": "ocid1.datasciencemodel.oc1.iad.<ocid>", 
                           "gpu_count": 1}, 
                         {"model_id": "ocid1.datasciencemodel.oc1.iad.<ocid2>", 
                          "gpu_count": 1}]'

The new model is called "model_group_YYYYMMDD", and has the freeform tags

multimodel: true
OCI_AQUA: active

The custom metadata added in this model are:

deployment-container: odsc-vllm-serving
model_group_count: 2
model-id-0: ocid1.datasciencemodel.oc1.iad.<ocid>
model-name-0: tiiuae/falcon-7b
artifact_location-0: oci://service-managed-models@<namespace>/service_models/falcon-7b/898df13/artifact
model-id-1:  ocid1.datasciencemodel.oc1.iad.<ocid>
model-name-1: phi-2
artifact_location-1: oci://service-managed-models@<namespace>/service_models/phi-2/b10c3eb/artifact