upgrade dependency image mu-python-template to releases v2.0.0-beta.2 (at least)

[marc-portier]

We noticed that the start.sh from the previous base docker-FROM-image throws a warning in the logs

./start-bad.sh: line 4: [: =: unary operator expected

Which is caused by the fact that the MODE environment variable is not set

The quick-hack around at out end is to simply add the environment MODE = "anything_but_development" via .env or docker-compose.yml

However, we noticed a newer version (v2.0.0.-beta.2) of mu-python-template is available that attempts to solve this case by mu-semtech/mu-python-template@bb0afbf

Alternatively a more complete fix and a new v2.0.0.-beta3 release could be considered. That could support even setting MODE="anything but development" as described in mu-semtech/mu-python-template#22