Config option for when transactions are marked as failed (event.outcome=failure)

[sorenlouv]

Problem
Today APM agents automatically mark http transactions as failed (event.outcome=failure) when http.response.status_code > 499. Some users want to treat other status codes like 4xx as failures as well. The only way to achieve that currently is by manually marking those transactions as failed. This is quite combersome for users that want to keep manual instrumentation to a minimum.

Describe the solution you'd like
It would be better if there was a config option for configuring which transactions were marked as failures. For instance a regex to match against http.response.status_code.

[sorenlouv]

Duplicate of #482