[gRPC/protoc] Support for Kotlin code generation

[FWest98]

Description

protoc supports Kotlin-specific code generation (https://protobuf.dev/reference/kotlin/kotlin-generated/) which helps a lot in the development experience: it generates a convenient DSL so the cumbersome builders are no longer needed. This Kotlin support is on top of the normal Java codegen output, and it would be great if this Kotlin-specific code can be generated in some way through Quarkus automatically.

Note that this is different from #24505, as this is only about the DSL (and related code) generated by protoc.

Implementation ideas

Some thoughts on what might work for this:

• Automatically set this option based through the quarkus-kotlin library; for example by letting this library influence some configuration in the code generation.
• Expose some option to toggle the creation of Kotlin sources
• Expose a more generic interface to "add parameters" to the protoc call.

[quarkus-bot]

/cc @alesj (grpc), @cescoffier (grpc), @geoand (kotlin)

[cescoffier]

it is still something we want to do, but it's not prioritized yet. Contributions are more than welcome.