INT-3337: `MongoDbMessageStore` Refactoring

JIRA: https://jira.spring.io/browse/INT-3337

INT-3337: Addressing PR comments

INT-3337: Add support to store/read Messages

* Add support to store/read `ErrorMessage`. As a trick for `Throwable` is selected (de)serializing converter

INT-3337: Add converters for `Message<?>` impls

INT-3337: Make `MDbMS.MessageWrapper` AuditAware

Add `_id` persistence field

Addressing PR comments

Polishing

- Docs
- Check for null ApplicationContext
- Add afterPropertiesSet() to tests