Update MODULE.bazel.lock file as part of Copybara workflow

We are using copybara this to push a set of common Bazel files into several other repositories. Some updates require updating the lock file in each of these destinations. We use `git.github_pr_destination` to push all modifications as single PR. Ideally the lock file update could be included there, i.e. something like a "bazel run" transformation would be nice. I couldn't find a way to do it in the examples/docs.

At minimum, I would like to run `bazel mod deps` to update the `MODULE.bazel.lock` file. A bonus would allowing me to run an arbitrary Bazel target (eg., `bazel run //foo`) as part of `after_migration`.