Support HTTP Request Body extraction

[bruno-garcia]

This feature exists in other SDKs and is configured like this:

An option named maxRequestBodySize.

The values are:

• never: request bodies are never sent (default)
• small: only small request bodies will be captured where the cutoff for small depends on the SDK (typically 4KB)
• medium: medium and small requests will be captured (typically 10KB)
• always: the SDK will always capture the request body for as long as Sentry can make sense of it

If opting-in means the request stream need to be buffered, that should be transparent. Docs can mention this caveat but it's fair to assume that if you're looking to get the request body included in error
s, you're not running a server that's about to tip over and you can afford having the payload buffered.

• [Document the feature spec in the develop docs](Add to the spec as "Expected Features": https://develop.sentry.dev/sdk/features/)

The code can depend on a simple HTTP abstraction to get the data.. That was needed in .NET to support both ASP.NET and ASP.NET Core.
Also: 1, 2

This feature was requested in #331 particularly for application/json.

[marandaneto]

Dart is also adding MaxRequestBodySize, so u may have a look at it too https://github.com/getsentry/sentry-dart/pull/473/files