Attach request body for more MIME types

[adinauer]

Problem Statement

Currently Sentry filters by MIME type when attaching the request body to an event, only doing so for JSON.

A user asked for this in #3641 (comment)

form-urlencoded requests are also used a lot, so I would like to support for “application/x-www-form-urlencoded”.

Solution Brainstorm

Python attaches JSON, form and files, see https://github.com/getsentry/sentry-python/blob/master/sentry_sdk%2Fintegrations%2F_wsgi_common.py#L129-L143.

We can extend from only JSON to more in v8.