GH-3501: Add GraphQL support

Fixes https://github.com/spring-projects/spring-integration/issues/3501

* make current with latest changes in 'spring-graphql'
* fix checkstyle issues
* implement reactive endpoint for GraphQL Query
* refactor to handle GraphQL Query and Mutation requests
* refactor to handle GraphQL Subscription requests
* implement expressions to handle for various RequestInput parameters
* convert classes to records in tests, remove unneeded datatype modifiers on channels
* replace executionId with idExpression SpEL evaluator
* adjust name and default expression for executionId
* rename for consistency, remove unneeded null check
* Clean up code style
* Remove redundant variables
* Add `What's New` entry
* Add `package-info.java`

src/reference/asciidoc/graphql.adoc

@@ -0,0 +1,23 @@
+[[graphql]]
+== GraphQL Support
+
+Spring Integration provides support for GraphQL.
+
+You need to include this dependency into your project:
+
+====
+[source, xml, subs="normal", role="primary"]
+.Maven
+----
+<dependency>
+    <groupId>org.springframework.integration</groupId>
+    <artifactId>spring-integration-graphql</artifactId>
+    <version>{project-version}</version>
+</dependency>
+----
+[source, groovy, subs="normal", role="secondary"]
+.Gradle
+----
+compile "org.springframework.integration:spring-integration-graphql:{project-version}"
+----
+====

src/reference/asciidoc/index-single.adoc

@@ -41,6 +41,8 @@ include::./ftp.adoc[]
 
 include::./gemfire.adoc[]
 
+include::./graphql.adoc[]
+
 include::./http.adoc[]
 
 include::./jdbc.adoc[]

src/reference/asciidoc/index.adoc

@@ -30,6 +30,7 @@ This documentation is also available as single searchable link:index-single.html
 <<./file.adoc#files,File Support>> ::
 <<./ftp.adoc#ftp,FTP/FTPS Adapters>> ::
 <<./gemfire.adoc#gemfire,Pivotal GemFire and Apache Geode Support>> ::
+<<./graphql.adoc#graphql,GraphQL Support>> ::
 <<./http.adoc#http,HTTP Support>> ::
 <<./jdbc.adoc#jdbc,JDBC Support>> ::
 <<./jpa.adoc#jpa,JPA Support>> ::

src/reference/asciidoc/whats-new.adoc

@@ -17,6 +17,12 @@ In general the project has been moved to Java 17 baseline and migrated from Java
 [[x6.0-new-components]]
 === New Components
 
+[[x6.0-graphql]]
+=== GraphQL Support
+
+The GraphQL support has been added.
+See <<./graphql.adoc#graphql,GraphQL Support>> for more information.
+
 [[x6.0-general]]
 === General Changes