Micronaut Discovery Client 3.0.0-M1

• bump up micronaut to 3.0.0-M4
• replace javax.inject with jakarta.inject
• remove @immutable ocurrences
• internals use Project Reactor instead of Rx Java 2
• replace nullability annotations
• Replace deprecated Jackson PropertyNamingStrategy

• oracle cloud vault code has been moved to the micronaut-oracle-cloud repository