[TASK] Support more file types in the .editorconfig

[oliverklee]

Now we also have formatting options for YAML and JSON files.

[JakeQZ]

Shouldn't it be 4 spaces indent for .json?

[JakeQZ]

Also noticed the 4 spaces indent already here for .md. Aren't we indenting .md with 2 spaces (e.g. bulleted lists in README)? Or have we not really decided?

[oliverklee]

I think we have not really decided. :-)

• https://www.markdownguide.org/basic-syntax/ does not say anything about indentation styles.
• https://markdown-guide.readthedocs.io/en/latest/basics.html says "4 spaces"
• https://google.github.io/styleguide/docguide/style.html also says 4 spaces

We might need to reformat our markdown files after this.