Add an unhandledRejection callback in the examples and the documentation

[massi-ang]

The StreamManagerClient constructor implicitly calls the asynchronous method _connect() to the stream manager service. If the connection fails, the promise is rejected, and must be caught via an unhandledRejection callback (https://nodejs.org/api/process.html#process_event_unhandledrejection).

This information should be added to the documentation of the StreamManagerClient.

aws-greengrass-core-sdk-js/aws-greengrass-core-sdk/stream-manager/client.js

Lines 38 to 44 in 0dcbd0b

	* @example <caption>StreamManager Usage</caption>
	* const { StreamManagerClient } = require('aws-greengrass-core-sdk/stream-manager');
	* const client = new StreamManagerClient();
	* c.onConnected(async () => {
	* // Do work with the client (c) here.
	* });
	*/

const client = new StreamManagerClient();

process.on('unhandledRejection', (reason, promise) => {
  console.log('Unhandled Rejection at:', promise, 'reason:', reason);
  // Application specific logging, throwing an error, or other logic here
});

client.on('connected', () => {
}
);