add support for application/graphql-response+json content type (#1699)

### 📝 Description
Based on the accept header, spring server respond either with `application/json` (default) or `application/graphql-response+json` media type.

### 🔗 Related Issues
#1573

Author: gumimin

servers/graphql-kotlin-spring-server/src/main/kotlin/com/expediagroup/graphql/server/spring/GraphQLRoutesConfiguration.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2021 Expedia, Inc
+ * Copyright 2023 Expedia, Inc
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,11 +20,11 @@ import com.expediagroup.graphql.server.spring.execution.SpringGraphQLServer
 import org.springframework.context.annotation.Bean
 import org.springframework.context.annotation.Configuration
 import org.springframework.context.annotation.Import
+import org.springframework.http.MediaType
 import org.springframework.web.reactive.function.server.ServerRequest
 import org.springframework.web.reactive.function.server.bodyValueAndAwait
 import org.springframework.web.reactive.function.server.buildAndAwait
 import org.springframework.web.reactive.function.server.coRouter
-import org.springframework.web.reactive.function.server.json
 
 /**
  * Default route configuration for GraphQL endpoints.
@@ -45,8 +45,14 @@ class GraphQLRoutesConfiguration(
 
         (isEndpointRequest and isNotWebSocketRequest).invoke { serverRequest ->
             val graphQLResponse = graphQLServer.execute(serverRequest)
+            val acceptMediaType = serverRequest
+                .headers()
+                .accept()
+                .find { it.includes(MediaType.APPLICATION_GRAPHQL_RESPONSE) }
+                ?.let { MediaType.APPLICATION_GRAPHQL_RESPONSE }
+                ?: MediaType.APPLICATION_JSON
             if (graphQLResponse != null) {
-                ok().json().bodyValueAndAwait(graphQLResponse)
+                ok().contentType(acceptMediaType).bodyValueAndAwait(graphQLResponse)
             } else {
                 badRequest().buildAndAwait()
             }

servers/graphql-kotlin-spring-server/src/test/kotlin/com/expediagroup/graphql/server/spring/routes/RouteConfigurationIT.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 Expedia, Inc
+ * Copyright 2023 Expedia, Inc
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -192,6 +192,19 @@ class RouteConfigurationIT(@Autowired private val testClient: WebTestClient) {
             .verifyGraphQLRoute("Hello POST application/graphql!")
     }
 
+    @Test
+    fun `verify POST graphQL request with application graphql response content type`() {
+        testClient.post()
+            .uri("/graphql")
+            .accept(MediaType.APPLICATION_GRAPHQL_RESPONSE)
+            .contentType(graphQLMediaType)
+            .bodyValue("query { hello(name: \"POST application/graphql\") }")
+            .exchange()
+            .expectHeader()
+            .contentType(MediaType.APPLICATION_GRAPHQL_RESPONSE)
+            .verifyGraphQLRoute("Hello POST application/graphql!")
+    }
+
     @Test
     fun `verify POST request with XML content type will result in HTTP 400 bad request`() {
         testClient.post()