Add kogan lx-8 support

[ewandank]

Adds support for the Kogan LX-8 Vacuum. Very similar to the Kogan LX-10, so i am guessing that the error messages are the same. I can remove those if that is preferred.

[ewandank]

I've had a closer look and it looks like i had an older version checked out, my apologies. It's now the same as lx-10 with a few fields marked as optional and the fanmode difference. I have pasted the output of tinytuya below. If there's a neater way to combine the lx-8 and lx-10 please let me know.

            "109": {
                "code": "funmode",
                "type": "Enum",
                "values": {
                    "range": [
                        "quiet",
                        "standard",
                        "strong"
                    ]
                }