feat: Make serializer configurable via YAML configuration

[lenchester]

This change enables users to specify custom serializers with configuration
options in their Enqueue bundle YAML configuration, improving flexibility
when working with different message formats.

• Add support for configuring serializers through YAML in RdKafkaContext
• Allow serializer specification as a class name, array with options, or instance

[lenchester]

@Steveb-p can you review the PR?

[lenchester]

Hmm, I’m not sure whether the error was caused by my changes.

[Steveb-p]

Hmm, I’m not sure whether the error was caused by my changes.

Seems like it was a one-off failure in one job in tests.