Handle unknown endpoints in error budgets

We have endpoints that are classified as unknown and do not contribute to a group's error budget.

It's unlikely that we will have 100% ownership of endpoints, but we need better awareness of the unknown enpoints and the traffic share that they account for.

The purpose of this issue is to:

• document what an unknown endpoint means
• generate a list of the current unknown endpoints
• determine for each unknown endpoint if it should be owned, allocated in a different way, or remain unknown.