chore: add `//bzlmod:hello_world_test` and use it as BCR presubmit (#2347)

- Create `bzlmod/hello_world` package based upon
`examples/bzlmod/hello_world`.
- Add `rules_bazel_integration_test` so that `//bzlmod:hello_world_test`
can be executed as a test from the parent workspace.
- Add `filegroup` targets named `all_files` to collect files for all of
the packages that are necessary to use `rules_rust`. These are an input
to the `rules_bazel_integration_test` test.
- Replace `.bcr/presubmit.yml` to test `//bzlmod:hello_world_test`.
- Update CI to test `//bzlmod:hello_world_test`.

Related to
https://github.com/bazelbuild/bazel-central-registry/pull/1199#discussion_r1429129814.