Add the `markdown-svgbob` extension

[llucax]

What's needed?

We need to render ASCII-art diagrams and graphs more nicely in the documentation.

Proposed solution

Add the markdown-svgbob extension.

TODO

• Add the extension
• Add the bob code block file type to any ASCII-art in the repo

Use cases

Be able to have diagrams / graphs that are readable both as text (when looking at docstrings in IDEs) and look nice in HTML documentation.

Alternatives and workarounds

No response

Additional context

PR adding this to Channels:

• Add some useful mkdocs extensions frequenz-channels-python#244