Reactive Programming - resilience4j

This product is used by exchanges with sometimes massive traffic / load and number of concurrent users, one performance issue somewhere can cripple instance completely. For this we have reactive programming and circuit breakers / bulkd heading. Introduce resilience4j to the project for high concurrent users scenarios to protect the instance and not cause cascading failures.

Ideally we should make it an optional configuration parameter since some exchanges DO NOT HAVE ability to run reactive sidecars.

Start by reviewing the cardano-rosetta-java architecture and identifying the high-concurrency paths and existing configuration mechanisms. Done means resilience4j support protects against cascading failures while remaining optional for exchanges that cannot run reactive sidecars.

Written by the indexing model from the issue text.