Check request json and form bodies with rack 3

[sl0thentr0py]

Rack 3 no longer requires rewindable input so check that we're still working gracefully and add data properly wherever possible.
https://github.com/rack/rack/blob/main/UPGRADE-GUIDE.md

We're relying on this here:

sentry-ruby/sentry-ruby/lib/sentry/interfaces/request.rb

Line 77 in 9446a30

request.body.rewind

[sl0thentr0py]

reference discussion
rack/rack#1972