Allow entering text directly instead of uploading a file for the agenda

[aaronpk]

Description

It would save a step to have a text field for editing an agenda inline instead of having to first create a file on my computer and upload it.

Code of Conduct

• I agree to follow the IETF's Code of Conduct

[rjsparks]

We have a similar field for entering reviews - we can provide one here - but be wary - it is only really usable for cut-paste - we don't have keystrokes being stored serverside (or even in a cookie) while editing, so a closed browser tab will lose any typing work.

[aaronpk]

That's perfectly fine, thanks! This will also help make quick edits to the agenda a lot easier!