Feature Request: Custom Audit Support

[chrisrink]

trafficstars

Feature Request: An configuration property to use a custom configuration that uses custom gatherers and audits per:

https://github.com/GoogleChrome/lighthouse/tree/304bbec53213ef0e8f027155d01ab2fd27b33135/docs/recipes/custom-audit

Probably need to add an option for configPath and then update pwmetrics/lib/metrics/metrics-adapter.ts to pass the custom metrics through.

I know this is a variant of https://github.com/paulirish/pwmetrics/issues/180 but It thought I would bring it up again.

[denar90]

@chrisrink are you interested in opening PR? I'll be more than happy to have it)