Add devcontainer definition for k3d kubernetes cluster (minikube alternative)

[kforeverisback]

Description

Add a new devcontainer definition for k3d kubernetes cluster.

With this, user will be able to create a new devcontainer which will enable the creation of a local kubernetes cluster (automated or manual).

This PR is based off of kubernetes-helm-minikube dev container.

PR Checklist

• [X] I have updated the documentation accordingly.
  • [X] Added README.md describing the container
  • [X] Added sample nginx deployment document in README.md
• [X] I have added/updated tests to cover my changes.
  • [X] Changed test.sh under test-project directory
• [X] All new and existing tests passed.
• [X] My code follows the code style of this project.
• [X] I have checked to ensure there aren't other open Pull Requests for the same update/change.
• [ ] Lint checker not integrated but fixed most Markdown and devcontainer.json lint errors (followed existing container document format)

Does this introduce a breaking change?

• [ ] Yes
• [X] No

Testing

• [X] Manually created Codespaces from .devcontainer
  • [X] Provisioned a k3d cluster from terminal
  • [X] Automatically provisioned k3d cluster in postStartCommand
• [X] Manually created local devcontainer
  • [X] Provisioned a k3d cluster from terminal afterwards
  • [X] Automatically provisioned k3d cluster in postStartCommand
• [X] Manually applied pods/deployments to verify k3d cluster

Isse Closes/Fixes

• Closes https://github.com/microsoft/vscode-dev-containers/issues/1455

[kforeverisback]

@iamnicoj @sivamu @juzuluag

[bamurtaugh]

Thanks so much for this contribution!

As a heads up, we're working on how to best support current and future contributions to this repo. As this poses a delay in accepting some new definitions, we want to emphasize we really appreciate your work, and we're working on how to best support contributions in a scalable way moving forward. There are additional details in this issue: https://github.com/microsoft/vscode-dev-containers/issues/1291.

[bamurtaugh]

Thanks again for opening this PR!

As a heads up, our team has been actively focused on an updated plan for community contributions and this repo moving forward, which we've now outlined in this issue: https://github.com/microsoft/vscode-dev-containers/issues/1589. This includes moving to a couple new repos for images (https://github.com/devcontainers/images) and Features (https://github.com/devcontainers/features).

We anticipate to have a similar repo and distribution process for templates/definitions. We'll keep everyone updated (likely via another issue in this repo or comment on https://github.com/microsoft/vscode-dev-containers/issues/1589) when our new templates repo is available and the process is defined.

Please let me know if you have any questions, thank you!