Add missing BUILD.bazel for K8s backend.
Add missing BUILD.bazel for K8s backend.

http://b/249217948

Change-Id: I37e2f65ee1611a72e9de3dc503f5a705ac54bd88
GitOrigin-RevId: d37d2a279eb99dd9e189a2816a5c20bdfa91431b

googlecloudrobotics/core,googlecloudrobotics/core,googlecloudrobotics/core