Use SerDes for H2 storage of retained messages

Release notes

[rn:skip]

Switch serializer of Retained messages in H2 store to also handle MQTT properties. Implement a new H2 DataType for Retained Message.

[x] My code follows the style guidelines of this project
[x] I have commented my code, particularly in hard-to-understand areas
~~[ ] I have made corresponding changes to the documentation~~
~~[ ] I have made corresponding change to the default configuration files (and/or docker env variables)~~
~~[ ] I have added tests that prove my fix is effective or that my feature works~~
~~[ ] I have updated the Changelog if it's a feature or a fix that has to be reported~~