[AIRFLOW-5704] Improve Kind Kubernetes scripts for local testing

[potiuk]

• Fixed problem that Kubernetes tests were testing latest master
  rather than what came from the local sources.
• Kind (Kubernetes in Dcocker) is run in the same Docker as Breeze env
• Moved Kubernetes scripts to 'in_container' dir where they belong now
• Kubernetes cluster is reused until it is stopped
• Kubernetes image is build from image in docker already + mounted sources
• Kubectl version name is corrected in the Dockerfile
• KUBERNETES_VERSION can now be used to select Kubernetes version
• Running kubernetes scripts is now easy in Breeze
• We can start/recreate/stop cluster using ---kind-cluster
• Instructions on how to run Kubernetes tests are updated
• The old "bare" environment is replaced by --no-deps switch

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Issue link: AIRFLOW-5704

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• Commit message/PR title starts with [AIRFLOW-NNNN]. AIRFLOW-NNNN = JIRA ID^*
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• Relevant documentation is updated including usage instructions.
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^* For document-only changes commit message can start with [AIRFLOW-XXXX].

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[potiuk]

@ashb @dimberman @gerardo -> I merged all the smaller PRs separated out from the Kind change and I am working on making the tests work for this one. While trying to fix and tests the kubernetes tests I noticed how difficult it was to iterate and re-test Kubernetes tests, so this one is now optimising even more:

1. Only the basic image for CI is built outside and sent to the docker. It is sent via untarred folder rather than as whole file. This makes it much nicer for the slow Mac Host->Docker volume mounting because the untarred image save contains separate .tars for all Docker image layers. I sync the layer dir via rsync based on checksum - this way I make sure than whenever the CI image is rebuilt, only the last rebuilt layers are changed. Then when the image is imported to DinD only the last layers are updated. this way while the environment is up and running and images are loaded to DiND and cluster, only incremental changes will be loaded.

2. Then I came back to building the kubernetes image inside breeze container. I will speed it up more, but it is actually much better for iterating when you are inside the breeze container. In order to reload last image to the cluster you will just need to run "rebuild_ariflow_image.sh" inside the container and it will (incrementally of course) rebuild and sent the new image layers to DiND and then to cluster.

I am still working on fixing the tests but I think it is much more developer-friendly than before.

[davlum]

I'm getting an error /opt/airflow/scripts/ci/in_container/kubernetes/app/deploy_app.sh: line 78: AIRFLOW_CI_KUBERNETES_IMAGE: unbound variable when running ./breeze -K.

If that's a required argument it should fail up front.

[potiuk]

@nuclearpinguin @kaxil @mik-laj - one last final review and I'd love to merge it