Prepare for Gradle v8

[phreed]

I get the following error.

Using method NamedDomainObjectContainer<T>.invoke(kotlin.Function1) has been deprecated. This is scheduled to be removed in Gradle 8.0. Recompile your plugin against Gradle >= 6.8 Consult the upgrading guide for further information: https://docs.gradle.org/7.1.1/userguide/upgrading_version_6.html#using_NamedDomainObjectContainer_invoke_kotlin_Function1

The specific code fragment is

protobuf {
   generatedFilesBaseDir = "$projectDir/src/main/java"
   protoc { artifact = "com.google.protobuf:protoc:2.6.1" }
   plugins {
      id("grpc") { artifact = "io.grpc:protoc-gen-grpc-java:1.0.0-pre2" }
   }
}

The plugins closure is the problematic line.

[voidzcy]

This is actually a duplicate of #444. We can't really do a migrate without Gradle's latest org.gradle:gradle-kotlin-dsl artifact. See details in #444 (comment).