[docker in docker] Adds retries for docker daemon startup and cgroup nesting

[samruddhikhandale]

Ref: #634 and #660

Updates in this PR -

• 19c9892 adds retries for docker daemon startup
• We have seen errors like sed: couldn't flush stdout: Device or resource errors which fails to start docker.25d2e80 adds retries to fix such sed errors
• 4b2c9fc adds a workflow which runs 100 jobs for validating docker startup --> 50 jobs validates dockerd after the container is started, and 50 jobs validates within the onCreateCommand

Important Note: /usr/local/share/docker-init.sh which starts/retries dockerd is added to the entrypoint command. This command runs in the background and is not a blocking script for the container startup. Since it's in the background, onCreateCommand/postCreateCommand/postStartCommand could all start executing before docker is fully running. If it takes docker too long, that could introduce flakiness in those lifecycle scripts.

Opened devcontainers/spec#299 which requests a new semantics to have "blocking" entrypoints that the CLI waits for. This way we can ensure that docker is already up and running for the mentioned ^ lifecycle scripts and is available in the container.

[samruddhikhandale]

Note: The failing test will be fixed with #661

[joshspicer]

nice! This looks really reasonable and the 50 passing tests doesn't hurt 😉

[samruddhikhandale]

nice! This looks really reasonable and the 50 passing tests doesn't hurt 😉

@joshspicer **100 😛
See https://github.com/devcontainers/features/actions/runs/5967344918/job/16188845503?pr=669