add id to event elements

[JamesHutchison]

Add's element ID to the response returned to the server

It allows for logic like this:

def get_input_by_id(e: dict, input_id: str) -> dict:
    for input in e["target"]["elements"]:
        if input.get("id") == input_id:
            return input
    raise Exception(f"Input not found: {input_id}")

Currently, inputs can only be grabbed by their index which is brittle.