fixes client using unsupported version of Socket.IO protocols

[twick00]

• I have added an entry to docs/changelog.md

I defer to the @cs01 about what to add to the changelog here

Summary of changes

Issue #366

python-socketio released a new version that points to the new SocketIO v3. This is a major protocol update making v2 and v3 incompatible:

https://socket.io/docs/v3/migrating-from-2-x-to-3-0

TL;DR: due to several breaking changes, a v2 client will not be able to connect to a v3 server (and vice versa)

This PR pins the server to use >=4.6.1 of python-socketio which uses the v2 protocol, the same as what the client uses.

You can see a table that details the python-socketio version breakdown here.

Test plan

N/A

[twick00]

I should probably add a test for this but I'm not particularly familiar with python.

@cs01 What do you think/recommend here?

[cs01]

Good stuff, thanks. I just tested and confirmed it fixed it. Ideally there would be a more extensive end-to-end test to verify the websocket could be established in the browser, but this is fine to land like this.