Add support for gRPC

[aledbf]

Which issue this PR fixes:

fixes #2207

Temporal image: quay.io/aledbf/nginx-ingress-controller:0.345
The annotation nginx.ingress.kubernetes.io/grpc-backend: "true" is required to enable this feature.
If the gRPC service requires TLS then also add the annotation
nginx.ingress.kubernetes.io/secure-backends: "true"

[k8s-ci-robot]

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[aledbf]

Example nginx.conf

+            # In case of errors try the next upstream server before returning an error
+            proxy_next_upstream                     error timeout invalid_header http_502 http_503 http_504;
+
+            grpc_pass grpc://default-http-svc-80;
+
+            proxy_redirect                          off;
+
+        }

[aledbf]

This is failing because the new nginx image is not published yet

[zaa]

@aledbf logs part must be a typo, should not that be grpc?

[aledbf]

@zaa yes. I just opened a PR to fix this