Improve parsing of Selenoid capabilities from cap files

Improve parsing of Selenoid capabilities from cap files

• This resolves #1090

This should allow for easy parsing of the following cap-file example:

capabilities = {
    "screenResolution": "1280x1024x24",
    "selenoid:options": {
        "enableVNC": True,
        "enableVideo": False,
    },
}

(as seen from SeleniumBase/examples/capabilities/selenoid_cap_file.py)

A valid command-line arg for this should also be accepted. Eg:

pytest --cap-string='{"selenoid:options": {"enableVNC": true}}

• Also refresh Python dependencies:
  -- rich==10.15.1;python_version>="3.6"