Use FastAPI's native `StreamingResponse` for less dependencies. This
initially didn't work because I didn't include the additional header
specifying the content type, which is an event stream.
ref: N25B-110
Uses a template for Python .gitignore files found
[here](https://github.com/github/gitignore/blob/main/Python.gitignore).
The only change from default is adding the .idea/ folder to the ignored
list (which might not be preferred, we will have to find out).
The Python application exposes an endpoint /message for the UI to send
messages to.
It also exposes an SSE endpoint /sse for the UI to listen to. Every
second, the CB sends the current time to UI.
ref: N25B-107
ref: N25B-110
