feat: Implemented and tested `MongoDbStorageStrategy`

feat: Implemented and tested `MongoDbStorageStrategy`

- Beware: The version 4.0.0 of Spring Data MongoDB that is included in
  Spring Boot 3.0.x does not work with version 4.8.1 of the MongoDB drivers
  that are included. Therefore, the version of the drivers was downgraded
  to 4.7.2 - See:
  https://docs.spring.io/spring-data/mongodb/docs/current/reference/html/#compatibility.matrix
- Also tried an upgrade of Spring Boot from 3.0.0 to 3.0.1, but without
  luck.
- Beware: Spring Boot 3.x does not include an autoconfigured embedded
  version of MongoDB for testing. It removed the autoconfiguration for
  `de.flapdoodle.embed:de.flapdoodle.embed.mongo` !