[java/kotlin client] update graphql-kotlin client documentation

We completely rewrote `graphql-kotlin` client code in 4.0.0 release. Updating documentation to match the latest version.

Author: Dariusz Kuc

src/content/code/language-support/java-kotlin-android/client/graphql-kotlin.md

@@ -5,21 +5,20 @@ url: https://github.com/ExpediaGroup/graphql-kotlin/
 github: ExpediaGroup/graphql-kotlin
 ---
 
-GraphQL Kotlin provides a set of lightweight type-safe GraphQL HTTP clients. The library provides Ktor HTTP client and Spring WebClient based reference implementations as well as allows for custom implementations using other engines. Type-safe data models are generated at build time by the GraphQL Kotlin Gradle and Maven plugins.
+GraphQL Kotlin provides a set of lightweight type-safe GraphQL HTTP clients. The library provides Ktor HTTP client and Spring WebClient based reference implementations as well as allows for custom implementations using other engines. Jackson and kotlinx-serialization type-safe data models are generated at build time by the provided Gradle and Maven plugins.
 
-To generate Ktor based GraphQL client add following to your Gradle build file:
+To generate Jackson models that will be used with GraphQL Kotlin Spring WebClient, add following to your Gradle build file:
 
 ```kotlin
 // build.gradle.kts
-import com.expediagroup.graphql.plugin.generator.GraphQLClientType
 import com.expediagroup.graphql.plugin.gradle.graphql
 
 plugins {
     id("com.expediagroup.graphql") version $latestGraphQLKotlinVersion
 }
 
 dependencies {
-  implementation("com.expediagroup:graphql-kotlin-ktor-client:$latestGraphQLKotlinVersion")
+  implementation("com.expediagroup:graphql-kotlin-spring-client:$latestGraphQLKotlinVersion")
 }
 
 graphql {
@@ -28,61 +27,59 @@ graphql {
         endpoint = "http://localhost:8080/graphql"
         // package for generated client code
         packageName = "com.example.generated"
-        clientType = GraphQLClientType.KTOR
     }
 }
 ```
 
-By default, GraphQL Kotlin plugin will look for query files under `src/main/resources`. Given `helloWorld: String!` query we can add following `HelloWorldQuery.graphql` sample query to our repo:
+By default, GraphQL Kotlin plugins will look for query files under `src/main/resources`. Given `HelloWorldQuery.graphql` sample query:
 
 ```graphql
 query HelloWorldQuery {
   helloWorld
 }
 ```
 
-Plugin will generate following client code:
+Plugin will generate classes that are simple POJOs implementing GraphQLClientRequest interface and represent a GraphQL request. 
 
 ```kotlin
 package com.example.generated
 
-import com.expediagroup.graphql.client.GraphQLKtorClient
-import com.expediagroup.graphql.types.GraphQLResponse
+import com.expediagroup.graphql.client.types.GraphQLClientRequest
 import kotlin.String
+import kotlin.reflect.KClass
 
 const val HELLO_WORLD_QUERY: String = "query HelloWorldQuery {\n    helloWorld\n}"
 
-class HelloWorldQuery(
-  private val graphQLClient: GraphQLKtorClient<*>
-) {
-  suspend fun execute(requestBuilder: HttpRequestBuilder.() -> Unit = {}): GraphQLResponse<HelloWorldQuery.Result> =
-      graphQLClient.execute(HELLO_WORLD_QUERY, "HelloWorldQuery", null, requestBuilder)
+class HelloWorldQuery: GraphQLClientRequest<HelloWorldQuery.Result> {
+    override val query: String = HELLO_WORLD_QUERY
 
-  data class Result(
-    val helloWorld: String
-  )
+    override val operationName: String = "HelloWorldQuery"
+
+    override fun responseType(): KClass<HelloWorldQuery.Result> = HelloWorldQuery.Result::class
+
+    data class Result(
+        val helloWorld: String
+    }
 }
 ```
 
-We can then execute the client 
+We can then execute our queries using target client.
 
 ```kotlin
 package com.example.client
 
-import com.expediagroup.graphql.client.GraphQLKtorClient
+import com.expediagroup.graphql.client.spring.GraphQLWebClient
 import com.expediagroup.graphql.generated.HelloWorldQuery
 import kotlinx.coroutines.runBlocking
-import java.net.URL
 
 fun main() {
-    val client = GraphQLKtorClient(url = URL("http://localhost:8080/graphql"))
-    val helloWorldQuery = HelloWorldQuery(client)
+    val client = GraphQLWebClient(url = "http://localhost:8080/graphql")
     runBlocking {
-        val result = helloWorldQuery.execute()
+        val helloWorldQuery = HelloWorldQuery()
+        val result = client.execute(helloWorldQuery)
         println("hello world query result: ${result.data?.helloWorld}")
     }
-    client.close()
 }
 ```
 
-See [graphql-kotlin docs](https://expediagroup.github.io/graphql-kotlin/docs/getting-started) for additional details.
+See [graphql-kotlin client docs](https://opensource.expediagroup.com/graphql-kotlin/docs/client/client-overview) for additional details.