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: https://github.com/getsentry/sentry-ruby/blob/9446a30e56d16dff04c98593a251cecbe872e147/sentry-ruby/lib/sentry/interfaces/request.rb#L77

[sl0thentr0py]

reference discussion https://github.com/rack/rack/discussions/1972

[fcheung]

FYI i just tripped over this - I have a plain rack app that I run with Rack::Lint in development (which enforces things like not assuming input is rewindable)