MqttOverWSProvider only works with JSON messages

[brimworks]

Describe the bug
If the MqttOverWSProvider is used for implementing the PubSub interface, and a non-JSON message is published to a topic that it is subscribed to, the following warning is printed:

[WARN] 27:28.905 MqttOverWSProvider - Error handling message, Array [
  [SyntaxError: JSON Parse error: Unexpected identifier "non-json-input"],
  "non-json-input",
]

To Reproduce
Steps to reproduce the behavior:

import Amplify from '@aws-amplify/core'
import PubSub from '@aws-amplify/pubsub';
import { AWSIoTProvider } from '@aws-amplify/pubsub/lib/Providers';

Amplify.configure(config);
Amplify.addPluggable(new AWSIoTProvider({
    aws_pubsub_region: 'XXXX',
    aws_pubsub_endpoint: 'wss://XXXX-ats.iot.us-east-1.amazonaws.com/mqtt',
}));

PubSub.subscribe("non-json-topic").subscribe({
            next: msg => console.log("got", msg),
            error: err => console.log("Failed to subscribe: ", err),
            close: () => console.log("close"),
        });

Note that you will need to publish a non-JSON message to the MQTT queue on the non-json-topic.

Expected behavior
An option to disable JSON serialization/deserialization during publish and subscribe so these non-JSON messages can be properly handled.

[guszille]

@brimworks Do you know if this intends to be changed? Would help me a lot.

[brimworks]

@Zillaine I'm really not sure, but to overcome this problem, I've just been using my forked version of code :(.

[guszille]

@brimworks So I'll enjoy your version too, thanks for that :).

[elkaadka]

it's being a major issue for us
can't understand why they assume every message is a json message

[talaikis]

This issue is fired every time null message is published in order to delete retained message.

[ehtesham1996]

Ah just got into a use case where i don't want to send json from device as the module used is esp32 and i am not forcing myself to install json library over it because the memory is limited to 4kb. @brimworks is there a way i could use your version too ? i mean how should i install it via npm