Java: Add client configuration for subscribing to channels.

[Yury-Fridlyand]

Ref: valkey-io#1602 and valkey-io#1616 and valkey-io#1650

Tested manually with

    @Test
    @SneakyThrows
    public void basic_client() {
        BiConsumer<Object, Object> callback =
            (msg, context) -> System.out.printf("Received %s, context %s\n", msg, context);

        var regularClient =
                RedisClient.CreateClient(
                                RedisClientConfiguration.builder()
                                        .address(NodeAddress.builder().port(6379).build())
                                        .requestTimeout(3000)
                                        .subscriptionConfiguration(
                                                StandaloneSubscriptionConfiguration.builder()
                                                        .subscription(EXACT, "ch1")
                                                        .subscription(PATTERN, "chat*")
                                                        .callback(callback)
                                                        .build())
                                        .build())
                        .get();

        Thread.sleep(100500);
    }

And with redis-cli: publish ch1 $message

TODO (in scope of this PR):

• Complete docs

Next feature parts (other PRs):

• Handling received pushes - Java client: receive pubsub messages #385
• Sending messages - Add PUBLISH and SPUBLISH commands. #391
• Tests
• Examples

[acarbonetto]

I would move this logic to the client, and create & the subscriptions in the constructor. Then you can just use a getter here to grab the subscriptions.

Would reduce duplicate code below.

[Yury-Fridlyand]

PubSubSubscriptions is a protobuf class. It is a right place for that.

[acarbonetto]

seems like duplicate code

[Yury-Fridlyand]

Unfortunately I didn't find a wayt to move it to another function. Classes are different for standalone and cluster clients.

[acarbonetto]

feels like callback subscription configuration and queued configuration could be separate objects

[Yury-Fridlyand]

How do you see that?
Is it good enough?

        var regularClient =
                RedisClient.CreateClient(
                                RedisClientConfiguration.builder()
                                        .address(NodeAddress.builder().port(6379).build())
                                        .requestTimeout(3000)
                                        .subscriptionConfiguration(
                                                StandaloneSubscriptionConfiguration.builder()
                                                        .subscription(PubSubChannelMode.EXACT, "ch1")
                                                        .subscription(PubSubChannelMode.PATTERN, "chat*")
                                                                        //   from there
                                                        .build())
                                        .subscriptionCallback(callback) // I moved this
                                        .build())
                        .get();