Write integration tests between the pipeline and cloud functions in contrib/

[ajvb]

We should write tooling to support integration tests between the cloud functions in contrib/ and the pipeline code.

Some examples:

• Test that Guardduty findings get processed through Gatekeeper, get sent to bugzilla-alert-manager, and create a new bug
• Test that a new auth event for an unknown IP gets an alert from Authprofile and gets sent to slackbot-background

There is currently not emulator tool for Cloud Functions written in Go, but these functions are written as a library, so wiring up our own runner for them should be easy enough (this is also how some of the unit tests work for the cloud functions).