Some work might be getting done within a Rack response body. For example, when
ActionController::Streaming is used, or when a Rack app elects to stream a response.

The Rack SPEC doc actually defines the behavior in sufficient detail to wrap this
into the same Appsignal transaction.

Sadly, there is some work involved in supporting all the right methods, so just
"one-size-fits-all" wrapper will not quite work

and include Sinatra-related integration changes If there is an
exception within `call` of a Rack app, the body won't be
returned. And that will be the case 99% of the time. If that
happens we need to complete the transaction early to ensure
data is sent across, as there is no BodyWrapper to complete it
for us.

Some work might be getting done inside the body (like when serving a ZIP).
We want this work to paint properly on the sample waterfall in
the Appsignal UI, so surround those with `instrument`.

Co-authored-by: Tom de Bruijn <tom@tomdebruijn.com>

which - it would seem - requires another conditional, but it doesn't.

Add changeset so the change can be released and is shown in the
CHANGELOG.md file upon release.

I mistyped the titles for the events in my comment on the GitHub issue.
This is what I meant to type.