Proposal: disallow formatting in headings

[berot3]

I sometimes copy paste text from somewhere and it does this formatting in the title, like bold or italic:

## **this is a heading**

Im not sure, but at least for me this is not wanted. to clean this up it would be helpful if markdownlint could point this occurrences out.

this is probably similar to #1308

Thanks!

[Malix-Labs]

this is probably similar to #1308

It is adjacent but different

[Malix-Labs]

Partial formatting might be desired,
For example:

### Heading with an **important** word in it 

Total formatting might be more clearly an anti-pattern:

### **heading with everything formatted as bold**