[EPIC] Indexed Quota Enforcement

[jjbayer]

Implement the quota enforcement as described in https://develop.sentry.dev/ingestion/relay/transaction-span-ratelimits/.

The current rate limiting code has become hard to maintain because of the many different data types and categories and the relationships between them:

• One envelope item can match multiple data categories
• Some envelope items have a parent-child relationship which is not reflected in the envelope itself.

Introduce a structured data type to make rate limiting more declarative and less error prone. These types can then be used throughout processing, not just in rate limiting. This draft might be a good starting point, but figuring out the design details is part of the epic.

Tasks

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1. Design structured data types
2. Convert envelopes to structured data types and use them in rate limiting
3. Use structured types in all of processing
4. Use structured types to communicate with the store producer / store forwarder (requires serialization outside of processor, might be blocked on async processor work)
5. [optional] Use structured format for relay-to-relay communication.