Support custom metrics in the timeout middleware

[theburningmonk]

This is a Feature Proposal

Description

• Need a way to also track the occurrence of timeouts as a metric. Ideally a way to plug in datadog or newrelic clients to track custom metrics

[theburningmonk]

cc @onlyplo

[theburningmonk]

As I mentioned on the other thread, the simplest solution I can think of is to let you pass in a callback function, but let's carry on the discussed on the other thread.

[onlyplo]

Yo, the initial work i have done here: d4f873b already starts to extend the middleware with a custom callback function.

Will probably need to change the naming and some logic based on our discussions to split off custom logging and custom metrics into separate issues.

Happy for me to submit a PR for this?

[theburningmonk]

Sure, go for it!

[theburningmonk]

@onlyplo any update on this?