Stream `compute` endpoint results

Created by: rvantonder

Tracks progress for integrating the compute streaming component.

• main PR: https://github.com/sourcegraph/sourcegraph/pull/30661

Remaining TODOs:

• Process errors raised by compute and send appropriate errors/alerts on stream. There is no event type for compute errors yet.
• Hydrate repo info in the stream Event type. Because compute results on the GQL end use a repository resolver, and not just the repository name, the internal compute result type does not store repo info. On the streaming endpoint, we have no use for a repository resolver, and need to hydrate the repo name into the streaming result type (readily available via file matches, just not done yet).
• Implement a URL query param to limit result counts (analogous to display limit for search results)
• Add integration test for basic operation
• Consider adding feature flag when it's used by something?