Signed-off-by: Stefan Schmidt <stefan.schmidt@huawei.com>

Signed-off-by: Stefan Schmidt <stefan.schmidt@huawei.com>

This relies on the plantuml plugin/module so it also includes the
required extension and to simplify that, we switch to using a `conf.py`
file.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>