render markdown in `data.html.twig` template

[stephan-strate]

When using markdown in a fields label it is not rendered in eg. emails, even though its activated through markdown: true.

[pmoreno-rodriguez]

I wonder how some pull requests like this are not already integrated into the plugin. I have been able to verify that it works perfectly in all my themes, and it is such a small modification that I do not understand why it is not already integrated for the next version.

Good job @stephan-strate