feat: demonstrate continuous selective delivery

[alexeagle]

Ask Aspect Workflows to push a docker container image. It should be pushed from any green build on the main branch
when the container is changed by a commit.

I'm going to need some help wiring up auth for CCI and BK to work properly.

[aspect-workflows]

Test

⚠️ Buildkite build #413 failed.

Failed tests (1)

//.circleci:write_merged_config_test [k8-fastbuild] 🔗

💡 To reproduce the test failures, run

bazel test //.circleci:write_merged_config_test

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Format      Lint      Lint [.]

[kylecordes]

Very good to see an example of this on the way in. In the last couple of classes I was present in, the topic came up and had to be hand-waved over.