feat: validate teams.yml in the service catalog

feat: validate teams.yml in the service catalog

This adds validation for services/teams.yml that is part of the service catalog.

With this change we validate that for all teams specified in teams.yml that have a product_stage_group specified the stage group refers to a know group in the stage-group-mapping.jsonnet. The latter is automatically kept up to date.

We also validate the other way around: a stage group should have an entry in the teams.yml file or otherwise be ignored. It should be a deliberate decision. Otherwise we risk missing alerts for new groups. For example https://gitlab.com/gitlab-com/gl-infra/production/-/issues/18191 might have been noticed sooner if we already had an entry for this group.

fix: Add the duo_chat team so alerts get routed

For now they are just routed to #g_mlops-alerts, as a lot of the AI related alerts are right now. People are paying attention to that channel already.