Add quarkus-morphium (de.caluga) as an external extension

[Bardioc1977]

Add quarkus-morphium (de.caluga) as an external extension

quarkus-morphium is a Quarkus extension for Morphium,
a Java MongoDB ODM. Since Morphium 6.3.0 the extension is part of the main Morphium reactor
(de.caluga:quarkus-morphium), replacing an earlier standalone/Quarkiverse-adjacent repo that saw
little traffic.

• Maven coordinates: de.caluga:quarkus-morphium, published to Central since 6.3.0.
• CDI producer, type-safe @ConfigMapping configuration, @MorphiumTransactional declarative
  transactions with CDI lifecycle events, Dev Services (auto-starting MongoDB, optionally as a
  replica set), MicroProfile health checks, GraalVM native-image support.
• Full Jakarta Data 1.0 @Repository support via
  build-time Gizmo bytecode generation (query derivation, JDQL, Page/CursoredPage pagination,
  Stream/CompletionStage async queries) — a working MongoDB provider for the spec, not a
  partial implementation.
• Migration Runner (@MorphiumChangeUnit/@Execution/@RollbackExecution) with a changelog and
  distributed lock, for versioned schema/data migrations.
• Documentation: an Antora module in the reactor
  (quarkus-morphium/docs/)
  plus a runnable showcase application
  demonstrating every feature end to end.

extensions/morphium.yaml added per the third-party extension convention (own group ID, not
io.quarkiverse, per the Quarkiverse onboarding guidelines).