Multiple jars for pekko-grpc

[mdedetrich]

When using sbt-reproducible-build on pekko-grpc along with this PR #278 I get

[error] (codegen / reproducibleBuildsCheck) java.lang.IllegalStateException: Found multiple artifacts for jar with filenames pekko-grpc-codegen_2.12-1.0.0-RC2.jar, pekko-grpc-codegen-assembly-1.0.0-RC2.jar
[error] (scalapb-protoc-plugin / reproducibleBuildsCheck) java.lang.IllegalStateException: Found multiple artifacts for jar with filenames pekko-grpc-scalapb-protoc-plugin_2.12-1.0.0-RC2.jar, pekko-grpc-scalapb-protoc-plugin-assembly-1.0.0-RC2.jar

I think this may be another case of checking jars which have are not meant to be published and this being picked up by sbt-reproducible-build.

[raboof]

jars which have are not meant to be published

I think we do want to publish codegen (for 3rd-party build plugins like https://github.com/tjarvstrand/mill-akka-grpc/blob/ba0a71211eabb85ba10b5164e0b2f187d54eb96b/build.sc#L39) and protoc-plugin (to use the Akka gRPC codegen 'standalone' without using the Akka gRPC build plugin).

I'm not sure we need both the -assembly and the non--assembly artifacts, though - that might be worth looking into.

[raboof]

But aside from that, perhaps we can take into account the classifier when looking for the matching artifacts and make sure it works even when those should both be published.