Add a Kubernetes example with classic Ubuntu RBE

[aaronmondal]

The LRE Kubernetes example is fairly complex and isn't an ideal introduction to remote execution. This example simplifies the setup a bit and shows how users can import arbitrary RBE images as nativelink workers.

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This change is 

[bytes00000111]

cc @blakehatch @bytes00000111

Readable version of the docs at: https://github.com/aaronmondal/nativelink/tree/rbe-ubuntu/deployment-examples/kubernetes-classic

Reviewable status: 0 of 1 LGTMs obtained, and pending CI: Bazel Dev / ubuntu-22.04, Cargo Dev / macos-13, Cargo Dev / ubuntu-22.04, Remote / large-ubuntu-22.04, asan / ubuntu-22.04, docker-compose-compiles-nativelink (20.04), docker-compose-compiles-nativelink (22.04), integration-tests (20.04), integration-tests (22.04), macos-13, publish-image, ubuntu-20.04 / stable, ubuntu-22.04, ubuntu-22.04 / stable, windows-2022 / stable, zig-cc ubuntu-20.04, zig-cc ubuntu-22.04

Cool! I'll give it a try!