Updates and fixes for User Agent handling

[m-mcgowan]

Changes

• added SetAppUserAgent, which allows the application to provide a dictionary of app user agent properties. This is merged with the host user agent info.
• Sends the user agent info as the body of the hub.set request.
• Unit tests to verify the expected changes to the hub.set request

Testing

Test Setup:

• Circuitpython 8.x running on Adafruit nRF52840
• Notecard + Notecarrier F
• notecard directory from note-python library copied to CIRCUITPY/lib/notecard
• Notecard connected to a Notehub project

Test Script:

import board
import busio
import notecard

port = busio.I2C(board.SCL, board.SDA)
card = notecard.OpenI2C(port, 0, 0, debug = True)
card.SetAppUserAgent({"app":"myapp"})
req = {"req": "hub.set"}
rsp = card.Transaction(req)

Test Output:

code.py output:
{"body": {"os_family": "Adafruit Feather nRF52840 Express with nRF52840", "req_interface": "i2c", "os_name": "circuitpython", "os_platform": "nRF52840", "agent": "note-python", "req_port": 0, "os_version": "3.4.0", "app": "myapp"}, "req": "hub.set"}
{}

Notehub event:

    "req": "note.update",
    "file": "_env.dbs",
    "note": "_state_vars",
    ...
    "body": {
        ...
        "user_agent": {
            "agent": "note-python",
            "app": "myapp",
            "os_family": "Adafruit Feather nRF52840 Express with nRF52840",
            "os_name": "circuitpython",
            "os_platform": "nRF52840",
            "os_version": "3.4.0",
            "req_interface": "i2c",
            "req_port": 0
        }
    },
    ...

[bsatrom]

This is a nit pick, but why not something like new_req.update({'body': self.GetUserAgent()}) instead of these two lines?

[m-mcgowan]

Can't say I gave it much thought, although I prefer lower density code for readability, plus it's helpful to have the intermediate values available for debugging. I'll factor it together.