Migrate bazel build setup to use bzlmod

[shameekganguly]

🎉 New feature

Summary

Bazel is migrating away from the WORKSPACE setup for dependency management, which is replaced by bzlmod (https://bazel.build/external/migration).

This change makes bazel build for gz-msgs compatible with bzlmod, and is similar to gazebosim/sdformat#1493 which added bzlmod support for sdformat.

A couple notes:

• Some of the bazel tests had to be disabled since they depend on gz-common/testing which is not yet migrated to bzlmod. I will re-enable these tests once gz-common/testing is migrated to bzlmod.
• In order to break dependency from gz-bazel (previously used for the WORKSPACE bazel setup), I directly added the required helper methods from https://github.com/gazebosim/gz-bazel/blob/garden/skylark/protobuf.bzl to https://github.com/gazebosim/gz-msgs/blob/gz-msgs11/tools/gz_msgs_generate.bzl. (These methods are only used in gz_msgs_generate.bzl, so it is safe to remove protobuf.bzl once the WORKSPACE build setup is fully deprecated across all Gazebo projects.)

Test it

Checkout this branch, and then

$ bazel build :all
$ bazel test :all

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[mjcarroll]

Not for here, but we can probably start moving up on the bazel version.

[shameekganguly]

Yes, I'll bump bazel versions across the board once we have a stable bzlmod build in gz sim.

[shameekganguly]

The Windows CI failure is unrelated since we don't have Bazel build/tests running in CI yet.

[iche033]

just minor comment otherwise works for me