Support copy paste to web

[VojtaStanek]

Currently https://discoveryjs.github.io/discovery/ supports only file upload as input.

I use Insomnia as an API client and it would be highly beneficial to be able to quickly copy-paste the response to discovery.js interface without needing to save it as a file.

[Guria]

My Business Analytics team also ofthen has their json not in uploadable files (embedded in docs, emails, etc). They tend to use online JSON explorers that allow to paste JSON in a text field.

Would be great to have paste functionality in discovery, so that they will also be able to benefit from using it.

[lahmatiy]

"Paste from clipboard" button added on welcome page: