fix: remove host headers in GrpcConnection

https://gravitee.atlassian.net/browse/APIM-3675

src/main/java/io/gravitee/connector/http/HttpConnection.java

@@ -69,7 +69,7 @@ public class HttpConnection<T extends HttpResponse> extends AbstractHttpConnecti
         HOP_HEADERS = Collections.unmodifiableSet(hopHeaders);
     }
 
-    private HttpClientRequest httpClientRequest;
+    protected HttpClientRequest httpClientRequest;
     private final ProxyRequest request;
     private T response;
     private Handler<Throwable> timeoutHandler;

src/main/java/io/gravitee/connector/http/grpc/GrpcConnection.java

@@ -24,6 +24,7 @@
 import io.vertx.core.Future;
 import io.vertx.core.http.HttpClient;
 import io.vertx.core.http.HttpClientRequest;
+import io.vertx.core.http.HttpHeaders;
 import io.vertx.core.http.HttpMethod;
 import io.vertx.core.http.RequestOptions;
 
@@ -60,4 +61,12 @@ protected Future<HttpClientRequest> prepareUpstreamRequest(HttpClient httpClient
                 return httpClientRequest.setChunked(true);
             });
     }
+
+    @Override
+    protected void writeUpstreamHeaders() {
+        super.writeUpstreamHeaders();
+
+        // Remove host header because gRPC is HTTP/2
+        httpClientRequest.headers().remove(HttpHeaders.HOST);
+    }
 }