Cirrus config in Starlark

[abravalheri]

The guys from CirrusCI have been doing an amazing job in improving the ways people can re-use CI configurations.
Lately they have implemented a way of writing the Cirrus tasks in a language that is very similar to Python (Starlark): https://cirrus-ci.org/guide/programming-tasks/. More importantly this language allows "importing" stuff (and therefore sharing re-usable functions).

I personally have contributed porting the code for deep cloning in the PyScaffold repository, that is now available in their official helpers repository.

In the future, it might be a good idea for us to use Starlark too in our templates.

[FlorianWilhelm]

I have never heard of it but if it helps to reduce duplicate code and is still easy to read, it's a good thing.