feat: Support ModelMetadata endpoint

[rafvasq]

Motivation

KServe V2 API's ModelMetadata endpoint is not yet supported in the rest-proxy grpc-gateway.

Modifications

Extend grpc-gateway to include it in addition to the Infer call already implemented.

Result

Resolves #14 and kserve/modelmesh-serving#418

[Jooho]

simply tested this and I confirm that this work well

1. Without version

 curl -k https://example-onnx-mnist-modelmesh-serving.apps.jlee-test.oylv.p1.openshiftapps.com/v2/models/example-onnx-mnist
{"name":"example-onnx-mnist__isvc-b29c3d91f3", "versions":["1"], "platform":"OpenVINO", "inputs":[{"name":"Input3", "datatype":"FP32", "shape":["1", "1", "28", "28"]}], "outputs":[{"name":"Plus214_Output_0", "datatype":"FP32", "shape":["1", "10"]}]}  support-rest-endpoints  ~/temp/20230822_Test_repo/rest-proxy       

2. With version

curl -k https://example-onnx-mnist-modelmesh-serving.apps.jlee-test.oylv.p1.openshiftapps.com/v2/models/example-onnx-mnist/versions/1
{"name":"example-onnx-mnist__isvc-b29c3d91f3", "versions":["1"], "platform":"OpenVINO", "inputs":[{"name":"Input3", "datatype":"FP32", "shape":["1", "1", "28", "28"]}], "outputs":[{"name":"Plus214_Output_0", "datatype":"FP32", "shape":["1", "10"]}]}

[ckadner]

Thanks @rafvasq -- need a few updates for the go.mod dependencies. I get different generated results, without these updates

[ckadner]

Thanks @rafvasq -- did you also regenerate the protos?

With google.golang.org/grpc v1.51.0 and `` I do get slightly different generated code

https://github.com/kserve/rest-proxy/pull/26/files#diff-2858165aafcdd2fe79ab516a84060fb8645cd00e44a92f623f3a57fe4b3b569cR446

Note: "Your version" is my version using grpc v1.51.0 :-)

---

UPDATE:

I did not notice this earlier, but I actually had different versions of grpc-gateway when installing into the developer image:

[root@957b1461dbb7 app]# go get github.com/grpc-ecosystem/grpc-gateway/v2/protoc-gen-grpc-gateway
go: downloading github.com/grpc-ecosystem/grpc-gateway/v2 v2.18.0
go: downloading github.com/grpc-ecosystem/grpc-gateway v1.16.0
go: downloading google.golang.org/grpc v1.58.0

Although DialContext may be what we want, it should not make a difference based on the code I see in grpc-go/clientconn.go

// Dial creates a client connection to the given target.
func Dial(target string, opts ...DialOption) (*ClientConn, error) {
	return DialContext(context.Background(), target, opts...)
}

[ckadner]

/lgtm