Add Ballerina language and ballerina-graphql to language support (#1337)

* Add Ballerina language and ballerina-graphql to language support

* Add ballerina to slug-map

* Add example for Ballerina client

Author: ThisaruGuruge

src/content/code/language-support/ballerina/client/ballerina-graphql.md

@@ -0,0 +1,27 @@
+---
+name: ballerina-graphql
+description: The Ballerina Standard Library Package for consume GraphQL services.
+url: https://lib.ballerina.io/ballerina/graphql/latest
+github: ballerina-platform/module-ballerina-graphql
+---
+
+To run a `ballerina-graphql` client:
+
+- Download and install [Ballerina Language](https://ballerina.io/downloads)
+- Then run `bal run graphql_client.bal` to run the service, with with this code in the `graphql_client.bal` file:
+
+```ballerina
+import ballerina/graphql;
+import ballerina/io;
+
+type Response record {
+    record { string hello; } data;
+};
+
+public function main() returns error? {
+    graphql:Client helloClient = check new ("localhost:9090/graphql");
+    string document = "{ hello }";
+    Response response = check helloClient->execute(document);
+    io:println(response.data.hello);
+}
+```

src/content/code/language-support/ballerina/server/ballerina-graphql.md

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+---
+name: ballerina-graphql
+description: The Ballerina Standard Library Package for write GraphQL services.
+url: https://lib.ballerina.io/ballerina/graphql/latest
+github: ballerina-platform/module-ballerina-graphql
+---
+
+To run a `ballerina-graphql` hello world server:
+
+- Download and install [Ballerina Language](https://ballerina.io/downloads)
+- Then run `bal run graphql_service.bal` to run the service, with with this code in the `graphql_service.bal` file:
+
+```ballerina
+import ballerina/graphql;
+
+service /graphql on new graphql:Listener(9090) {
+    resource function get hello() returns string {
+        return "Hello, world!";
+    }
+}
+```
+
+## Features
+- Built with Ballerina `service` and `listener` model, which are first-class citizens in Ballerina
+- Supports subscriptions over websocket (No additional libraries needed)
+- Supports file upload
+- Built-in GraphiQL client

src/content/code/slug-map.json

@@ -1,4 +1,5 @@
 {
+  "ballerina": "Ballerina",
   "c-c": "C / C++",
   "c-net": "C# / .NET",
   "clojure": "Clojure",