Revert "Temporary disable grpc samples"

[mkurz]

This reverts commit 108c50c.

This grpc stuff needs more work...

[mkurz]

Also note, grep'ing for akka in the grpc examples:

play-java-grpc-example/build.sbt:  .enablePlugins(AkkaGrpcPlugin) // enables source generation for gRPC
play-java-grpc-example/build.sbt:    akkaGrpcGeneratedLanguages := Seq(AkkaGrpc.Java),
play-java-grpc-example/build.sbt:    akkaGrpcExtraGenerators += PlayJavaClientCodeGenerator,
play-java-grpc-example/build.sbt:    akkaGrpcExtraGenerators += PlayJavaServerCodeGenerator,
play-java-grpc-example/docs/src/main/paradox/code-details.md:The `AkkaGrpcPlugin` locates the gRPC `.proto` files and generates source code from it. Remember to enable the plugin
play-java-grpc-example/docs/src/main/paradox/code-details.md:### 2.a Serving (Akka) gRPC Services
play-java-grpc-example/conf/application.conf:  enabled += example.myapp.helloworld.grpc.AkkaGrpcClientModule

play-scala-grpc-example/build.sbt:  .enablePlugins(AkkaGrpcPlugin) // enables source generation for gRPC
play-scala-grpc-example/build.sbt:      akkaGrpcGeneratedLanguages := Seq(AkkaGrpc.Scala),
play-scala-grpc-example/build.sbt:      akkaGrpcExtraGenerators += PlayScalaClientCodeGenerator,
play-scala-grpc-example/build.sbt:      akkaGrpcExtraGenerators += PlayScalaServerCodeGenerator,
play-scala-grpc-example/docs/src/main/paradox/code-details.md:The `AkkaGrpcPlugin` locates the gRPC `.proto` files and generates source code from it. Remember to enable the plugin
play-scala-grpc-example/docs/src/main/paradox/code-details.md:### 2.a Serving (Akka) gRPC Services
play-scala-grpc-example/conf/application.conf:  enabled += example.myapp.helloworld.grpc.AkkaGrpcClientModule

[mkurz]

@ihostage Just FYI, we will need that one here later.

[ihostage]

Superseded by #492