Update embedding examples

The [internal_ipkernel.py](https://github.com/ipython/ipykernel/blob/main/examples/embedding/internal_ipkernel.py) and [ipkernel_qtapp.py](https://github.com/ipython/ipykernel/blob/main/examples/embedding/ipkernel_qtapp.py) are out of date. Some issues:

* It is using `PyQt4`, which is very old, and not supported on some platforms (e.g. `osx-arm64`)
* Explicit use of PyQt means it doesn't work with PySide. Should use [qtpy](https://github.com/spyder-ide/qtpy) so it will work with Pyside2/6 or PyQt5/6.
* This line: `from IPython.lib.kernel import connect_qtconsole` fails on recent ipythons. I think the replacement is `from ipykernel import connect_qtconsole`. See https://github.com/ipython/ipython/issues/13610
* The `connect` calls also would need to be updated (I think those are the old style signals).