[REQ] Add possibility to use KSP instead of KAPT

Is your feature request related to a problem? Please describe.

We generate client libraries for our app and we use moshi codegen. The problem is, that for a valid codegeneration we need KSP, but not KAPT, that is generated by default

Describe the solution you'd like

Maybe configuration flag like "moshiCodegenKsp": Boolean

Describe alternatives you've considered

No alternatives

Additional context

The thing is, that i wanted to introduce kotlin value classes into our generated models. Everything worked like charm in my test project, but i got wierd codegen in the real one. As it seems to me, the problem is, that my test project is using KSP for moshi codegen, but the library we ship is using kapt: i can see it in a generated build.gradle file. When i tested the theory, that KAPT might break my test project - it really broke it and i received the same error

Start by tracing the Kotlin client generation configuration and the generated build.gradle file mentioned in the issue. Determine where KAPT is enabled and how a configuration flag could select KSP, then verify that generated Moshi codegen projects build successfully with the selected processor.