Support for handling event/command metadata - application layer

[idugalic]

• EventRepository is extended with additional methods to support fetching and storing metadata of the event.

• StateRepository is extended with additional methods to support fetching and storing metadata.

• ViewStateRepository is extended with additional methods to support fetching and storing metadata.

• ActionPublisher is extended with additional methods to support publishing actions with metadata.

• Metadata is modeled as a Map<String, Any>.

• Metadata is restricted to the Application layer only. It is a Map. It can be anything/week contract. It does not leak into Domain. All the computations and decisions are done by only using a strong type of the payload/Event/E

Some examples of metadata:

• userId
• traceId
• eventRevision

NOTICE, how userId could be part of the formal Paylod Type/E/C in case authorization is a concern of the Domain core logic. SO, if you don't need these data to make domain core decisions put it in metadata, otherwise, it is part of the strongly typed payload type.

Aggregate/MaterializedView/SagaManager is enriched with new extensions to expose the handle API that can accept metadata as an additional parameter:

fun <C, S, E> EventSourcingAggregate<C, S, E>.handle(command: C): Flow<E> =
    command
        .fetchEvents()
        .computeNewEvents(command)
        .save()


fun <C, S, E> EventSourcingAggregate<C, S, E>.handle(
    command: C,
    metaData: Map<String, Any>
): Flow<Pair<E, Map<String, Any>>> =
    command
        .fetchEventsAndMetaData().map { it.first }
        .computeNewEvents(command)
        .saveWithMetaData(metaData)

This PR is not binary backwards compatible with previous version!