[py] Add copybara scripts (#8368)

These are the scripts I've been using to sync between mostrobotpy and
here. I debated putting it in the "source of truth" that is
`mostrobotpy` , but I think it makes more sense here since it already
has bazel set up, and I've also recently added the ability to sync the
`commands-v2` repository, so having it all in one copybara script makes
sense.

This includes a helper python script to make it a little bit easier to
run.

BUILD.bazel

@@ -1,4 +1,5 @@
 load("@aspect_bazel_lib//lib:write_source_files.bzl", "write_source_files")
+load("@rules_java//java:java_binary.bzl", "java_binary")
 load("@rules_pkg//:mappings.bzl", "pkg_files")
 load("@rules_python//python:pip.bzl", "compile_pip_requirements")
 load("//shared/bazel/rules:publishing.bzl", "publish_all")
@@ -41,6 +42,12 @@ alias(
     visibility = ["//visibility:public"],
 )
 
+java_binary(
+    name = "copybara",
+    main_class = "com.google.copybara.Main",
+    runtime_deps = ["@com_github_google_copybara//jar"],
+)
+
 # This is a helper to run all of the pregeneration scripts at once.
 write_source_files(
     name = "write_pregenerated_files",