Feature request: Aupport arbitrary headers in HTTP request

**Is your feature request related to a problem? Please describe.**
I was trying to use the HTTP request with an azure function which requires an `x-function-key` header, but I was confronted with the error message `HTTP request - TypeError in blob ... invalid header name`
I might have missed it, but I don't see an option anywhere to allow custom kind of headers

**Describe the solution you'd like**
Maybe my suggestion would be a simple checkbox on the http request node for allowing not to validate header names

**Describe alternatives you've considered**
Another alternative would be to simply disable validation overall without that checkbox, but that would probably be more intrusive on seasoned users

**Additional context**
none