build: Add Bazel java_grpc_library rule

Bazel third party dependencies are specified in repositories.bzl which
gives the consumer the ability to opt-out of any dependencies they use
directly in their own project.

Fixes #2756
diff --git a/WORKSPACE b/WORKSPACE
new file mode 100644
index 0000000..e0ae4f0
--- /dev/null
+++ b/WORKSPACE
@@ -0,0 +1,5 @@
+workspace(name = "grpc_java")
+
+load("//:repositories.bzl", "grpc_java_repositories")
+
+grpc_java_repositories()