Autogenerate routing tree based on feature categories

Introduction

There is a requirement for teams to receive service level alerts for the services that they are responsible for.

For example:

• An EM, @zj-gitlab, approached me saying "yesterday there was an incident involving one of our services. The Gitaly team would have liked to help out, but were unaware of the incident".
• The Pages team would live to be notified of pages service service-level degradations: #344 (closed)

Problem

Currently, our alert routing tree is quite adhoc. Additionally, its difficult to update to route alerts to a team.

Proposal

Using the feature_category attribute, and the service catalog, allow alerts that have the appropriate feature_category label to be routed to engineering teams, so that they can be aware of ongoing incidents.

Benefit/Impact

1. More self-service capability by teams to receive alerts they're interested in (MRs on the runbooks repo, presumably easily determined)
2. Broader understanding of the operational system by dev teams

Tasks

TBD