Add redux reducer for app updates websocket events

[siemiatj]

Is this a bug or feature request?

Feature

What is the current behavior?

Together with @metas-ts we've decided there must be a way of notifying the application about changes to data without altering the current UI. So plan is to have new websocket requests that will be stored in the app state available for the app to check.

Which are the steps to reproduce?

What is the expected or desired behavior?

Example flow (just to get the basic idea of what we're trying to accomplish) would be as follows :

• App registers itself to a websocket-topic "SalesOrder-{id}-ShipmentSchedules"
• User creates and then saves a new sales order
• Backend completes the sales order
• App waits for a "ShipmentSchedules" message from the websocket
• App unregisters from the websocket topic
• UI zooms to the shipment schedules

[siemiatj]

Websockets communication

1. Use the websocket server provided by https://www.websocket.org/echo.html
2. Metasfresh app is using the stompjs library for ws connections, but since STOMP format it's not supported by the websocket.org server, you can use ws, or any other package.
3. We have redux actions for connecting/disconnecting websockets (https://github.com/metasfresh/metasfresh-webui-frontend/blob/master/src/actions/WindowActions.js#L1327) as a general guidance, but for reasons mentioned above (and since you're gonna be using a different endpoint for communication) you have to create new ones
4. Returned websocket message should have a json format and two fields:

   {
   id,
   name,
   }

Where to start:

First, when creating your dev environment (https://github.com/metasfresh/metasfresh-webui-frontend/blob/master/README.md#dev-environment) point your configs to https://dev667.metasfresh.com/ instead of localhost. Credentials to authenticate are:

• user: devtest1234
• pass: demo1234

This is a dev instance with only basic test data added, so you can play around there without breaking things.

Implementation requirements

• new branch in the application state tree (redux) which stores open websocket connections
• app can check what connections are open & the number of open connections
• app can subscribe to websocket endpoint @ https://www.websocket.org/echo.html
• When a message { id: 1, name: 'Test' } is sent from the test server, app stores it in the redux state
• message is propagated to the UI (console.log, alert, any other form)
• app can unsubscribe from the websocket endpoint after successfully handling the message