Support binding text content to a string

[danroth27]

We support returning strings as text.

Seems like this should work for the request: Post([FromBody] string bodyText)

[yishaigalatzer]

We don't think it is a good idea to promote this pattern. The users can always write the formatter, but since we think most of the time this is a mistake we shouldn't put it in the framework.

This could go on a contrib style repo if someone finds it useful, but it shouldn't go out to the masses.