Add blacken-docs to pre-commit

[jorgepiloto]

Description of the feature

Something I discovered while working on #64 was that some of the code snippets were not compliant with the code style guidelines.

After looking for a solution, I came across blacken-docs, which turned out to be extremely useful.

Steps for implementing the feature

The main idea behind this new feature would be to add this doc style checker to our current style tests via pre-commit.

Useful links and references

Blacken-docs: https://github.com/asottile/blacken-docs/

[jorgepiloto]

⚠️ Notice some of our examples are non-style compliant on purpose

This is done to educate others on what to do and avoid. As long as blacken-docs can ignore these files, we can implement this feature.

[MaxJPRey]

@jorgepiloto I will implement it for PyAEDT. It should be even easier, because in this repo we shouldn't ignore any code samples.

[RobPasMue]

Working on this. I will also implement pre-commit.ci in this task if it's okay with you all.