Make essential Bazel packages publicly visible

This allows separate Bazel projects to reference Nomulus as an external
repository. They can then copy the []
directory structure into their own project and customize the Action
and Module lists for the GAE modules in their own deployment.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=136863886

java/google/registry/BUILD

@@ -16,6 +16,15 @@ package_group(
     ],
 )
 
+# Visibility group for rules that are //visibility:public on GitHub but project
+# scoped in Google's internal repository.
+package_group(
+    name = "public",
+    packages = [
+        "//visibility:public",
+    ],
+)
+