Centralizing Plugin Conversion with Plugin Code

Is your feature request related to a problem? Please describe.
Building plugins requires defining components of a plugin (core feature, logstash mapping) in multiple parts of the code base.

Users build their plugins in their specific plugin module in the data-prepper-plugins package. Here they implement the interface (source, prepper, sink) for the plugin type they are developing and define the configuration. To support Logstash conversion, plugin authors must create a separate classes in a separate module in the data-prepper-logstash-configuration package. This current approach scatters plugin concepts across the code base.

Describe the solution you'd like
Ideally, as a plugin author I would like to define my mapping and implementation details in the same package.

Describe alternatives you've considered (Optional)
I am open to alternatives...

Additional context
I think this is an important feature to consider as we build support for the community to bring their own plugins.

Start by comparing plugin implementations and configuration in data-prepper-plugins with the mapping classes in data-prepper-logstash-configuration/src/main/java/org/opensearch/dataprepper/logstash/mapping. Define the integration approach before changing code; done means plugin authors can keep implementation and Logstash mapping details in the same plugin package without scattering those concepts across modules.