Force tables to always have a header

[manuelleduc]

Is your feature request related to a problem? Please describe.
Often, markdown renderer expect a table to have a header.
Headers are not enforced by default in the editors. Consequently, when the content of the editor is serialized to Markdown, the result can lead to error, or to difference between what's shown is the editor, and what's shown in the content.

Describe the solution you'd like
My proposal is to introduce an option to force the tables to always have a header.

Additional context
This is somewhat related to #1377

Bonus
[ ] I'm a sponsor and would appreciate if you could look into this sooner than later 💖