Provide SPI for strategy and processor #7
Description
The generatorAPI is great for designing code from scratch. But if the overall result of teh generation is fixed (follows a kind of template), you might not want to start all over again.
Strategies can define a general code template that is generated from a given meta-input. Processors allow to hook into the generation process by enriching certain parts.
We had a concept for strategies, processors and SPI (service locators) in avro-kotlin generation already. We should move the general concept as a feature to this core generation lib and use it in other locations.