DiscoveryConfigChangeEvent implementation

[charlestp]

Implementation of new DiscoveryConfigChangeEvent defined in #69626

This implementation will replace the old DiscoveryConfigEvent. I made a new event since merging into the old event would result in a lot of confusing variations of fields. The new events carries more information that will be useful for product analysis.

• which client kind made it
• setup attempt ID so frontend events can be correlated all the way through to backend resource events.
• separate cloud providers and cloud resource types for easier joining and aggregation.
• enum types instead of strings

I'm planning to delete the old event in a follow-up PR.

setup_attempt_id will get plumbed through with the frontend events work in a follow-up PR.

Manual Test Plan

Test Environment

Locally

Test Cases

• New event is emitted with the expected fields