allow custom "DeviceCodePollUi" in OIDC device code flow

[soxofaan]

current support to show a "UI" to show device code instructions is basic text and Jupyter:

openeo-python-client/openeo/rest/auth/oidc.py

Lines 905 to 908 in 7d11a4e

	if in_jupyter_context():
	poll_ui = _JupyterDeviceCodePollUi(timeout=self._max_poll_time, elapsed=elapsed)
	else:
	poll_ui = _BasicDeviceCodePollUi(timeout=self._max_poll_time, elapsed=elapsed, display=self._display)

for other context, e.g. QGIS integration, it would be handy to allow injection of a custom implementation

[soxofaan]

cc @m-mohr