Project Config update reduction

[Dav1dde]

Project Config updates are quite costly within Relay but also in propagation over the wire. Project configs are consistently polled and kept up to date. The current mechanism/API has no way of indicating that a project config has not changed since the last update.

To reduce costs of these constant updates we should introduce a way to only actually send and update a project config when it changed.

For this to work we need to:

• Have a revision/hash of the project config. In an initial dumb implementation can just generate a new revision everytime the project config is recomputed. A more elaborate version of this can calculate a consistent hash/version of the project config.
• The API needs to be extended to allow signalling a project config was not updated, at the same time downstream Relays must be able to include their current revision ID per project config in the request.
• Processing Relays loading from Redis can be updated to read from a more lightweight key <project_config_key>.revision first and only read the full update when the revision is unlike the one currently held in the cache.

Tasks

Beta Give feedback

1. Remove sentry:relay-rev from Sentry and instead use a new id for every time the config is generated
2. Let Sentry write an additional Redis key for the revision
3. Update Relay to use the new Redis key
4. Extend the Project Config API in Relay
5. Extend the Project Config API in Sentry