[Feat] Plot image endpoint

[angel-penchev]

Describe the feature you'd like
Create an POST "/plot/<connection code>" endpoint, which accepts form-data containg only 1 field - image. It should search the database for a plotter with the same connection code, get the session id from there, get the socket by the session id and forward the image on the plotter.

Additional context

• The following code snippet might be helpful:
  const plotterSocket = io.sockets.sockets.get(sessionId);