Add licensing with rules_license

We have no licensing in this module. We can use rules_license can be used to apply licensing by providing Bazel rules for applying the licensing and propagating them through the build graph.

We should add an MIT license and register our it via the @rules_license//rules:license.bzl rule:

license(
    name = "license",
    ...
)

The license target should then be associated to all targets in the module in REPO.bazel

We have a done a similar thing in bazel/toolchain_utils