Reflection based experience

[slinkydeveloper]

New Restate SDK experience, based on reflections, to remove the friction of using the annotation processor based code generator.

Implementation consists of:

• Java support
• Kotlin support
• Spring boot Java support
• Spring boot Kotlin support

Once we have enough feedback, we can proceed to stabilization, which would include:

• Update examples to use the new API
• Update documentation to use new API
• Maybe GraalVM native image support #23 ?
• Phase out annotation processor?