Add document:mUpdate

[y-abs]

What does this PR do ?

This PR implements the mUpdate method with its unit tests.

How should this be manually tested?

Clone this branch and run unit tests
./gradlew test

When it succeed, compile it

./gradlew jar

Initiate another java project by adding the compiled SDK as a dependency.

Then, run Kuzzle, create an index nyc-open-data and a yellow-taxi collection in the admin console. Create 2 documents some-id1 and some-id2.
Finally, run this code

import io.kuzzle.sdk.*;
import io.kuzzle.sdk.Options.KuzzleOptions;
import io.kuzzle.sdk.Options.Protocol.WebSocketOptions;
import io.kuzzle.sdk.Protocol.WebSocket;

import java.util.concurrent.ConcurrentHashMap;

public class mUpdateDocument {
    private static Kuzzle kuzzle;

    public static void main(String[] args) {
        WebSocketOptions opts = new WebSocketOptions();
        opts.setAutoReconnect(true).setConnectionTimeout(42000);

        try {
            WebSocket ws = new WebSocket("localhost", opts);

            kuzzle = new Kuzzle(ws, (KuzzleOptions) null);

            kuzzle.connect();

            ConcurrentHashMap<String, Object> document1 = new ConcurrentHashMap<>();
            ConcurrentHashMap<String, Object> body1 = new ConcurrentHashMap<>();

            ConcurrentHashMap<String, Object> document2 = new ConcurrentHashMap<>();
            ConcurrentHashMap<String, Object> body2 = new ConcurrentHashMap<>();

            document1.put("_id", "some-id1");
            body1.put("key", "value");
            document1.put("body", body1);

            document2.put("_id", "some-id2");
            body2.put("key", "value");
            document2.put("body", body2);

            ArrayList<ConcurrentHashMap<String, Object>> content = new ArrayList<>();
            content.add(document1);
            content.add(document2);

            ConcurrentHashMap<String, Object> response =
            kuzzle.getDocumentController().mUpdate("nyc-open-data", "yellow-taxi", content)
            .get();

            System.out.println(response);
        }  catch (Exception e) {
            e.printStackTrace();
        }

        kuzzle.disconnect();
    }
};

You should see the documents updated.

[scottinet]

Seems to be copy-pasted from the document:create documentation: document identifiers are not optional for update methods.

[y-abs]

In deed