DE-1166: Run CircleCI jobs on self-hosted container runners

[bluepal-prasanthi-moparthi]

No description provided.

[Copilot]

Pull request overview

Switches CircleCI jobs from CircleCI-hosted machine executors to self-hosted Docker container runners (arangodb/medium-* resource classes), and introduces a setup-docker command that installs and starts dockerd inside the job container for jobs that need Docker. Also realigns workspace paths to the new container user/home and drops the now-unused setup_remote_docker steps.

Changes:

• Replace x86-machine-executor/arm-machine-executor with x86-docker-executor/arm-docker-executor (and add a resource_class to golang-executor), and remove setup_remote_docker from check-code and vulncheck.
• Add a setup-docker command (apt-installs docker.io if missing, starts dockerd in the background, waits up to 30s for it to become ready) and invoke it from run-unit-tests, run-integration-tests, and run-integration-tests-arm.
• Move download-demo-data to the golang-executor and switch the demo-resources path from $HOME/resources to /home/circleci/resources (matching the persist_to_workspace root used by the integration jobs).

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