feat: add websocket and query to servers API

[lorenzo-cavazzi]

This is a demonstration of how to set up a WebSocket channel using the ws package, and how to query other renku APIs with the axios library.

How to test: You need to create a user and login into the test deployment. From that page, open the developer console and create a WebSocket object:

webSocket = new WebSocket("wss://renku-ci-ui-1331.dev.renku.ch/ui-server");
webSocket.onmessage = function (event) {
    console.log('Message from server ', event.data);
};

You can now send messages using webSocket.send().

webSocket.send("test"); // get the message back -- work with any other text
webSocket.send("servers"); // get the number of running interactive environments

/deploy
re #1264

[RenkuBot]

You can access the deployment of this PR at https://renku-ci-ui-1331.dev.renku.ch

[lorenzo-cavazzi]

This will soon be closed and superseded by #1888 and #1904