Optional model version

The descriptions for "_Model Ready_" and "_Model Metadata_" in both the REST and gRPC specifications claim that the model version is optional. Is this true? If so, the specification should report it's optionality in more than a comment/description (`optional` in proto3 and `required: false` in openAPI). If the version is optional in the REST protocol, should there instead be another versionless route instead of eg, `'/v2/models/${MODEL_NAME}/versions/${MODEL_VERSION}/ready'`?

https://github.com/kserve/open-inference-protocol/blob/eeb043e2c95c1dd35f8b9185f5dadf44c7f10c9f/specification/protocol/open_inference_grpc.proto#L68-L70

https://github.com/kserve/open-inference-protocol/blob/eeb043e2c95c1dd35f8b9185f5dadf44c7f10c9f/specification/protocol/open_inference_grpc.proto#L98-L100

https://github.com/kserve/open-inference-protocol/blob/eeb043e2c95c1dd35f8b9185f5dadf44c7f10c9f/specification/protocol/open_inference_rest.yaml#L61

https://github.com/kserve/open-inference-protocol/blob/eeb043e2c95c1dd35f8b9185f5dadf44c7f10c9f/specification/protocol/open_inference_rest.yaml#L104

Read the referenced sections of specification/protocol/open_inference_grpc.proto and specification/protocol/open_inference_rest.yaml, focusing on the Model Ready and Model Metadata definitions and their versioned routes. Determine whether model versions are optional in both protocols and whether REST needs a versionless route. Done means the specification consistently records the decision in the relevant proto and OpenAPI definitions.

Written by the indexing model from the issue text.