Add rootless Docker support and update documentation

[sireeshajonnalagadda]

This PR fixes the issue for rootless docker

• Introduced socketPath option for custom Docker socket configuration in README and devcontainer-feature.json.
• Updated install script to accommodate rootless Docker socket paths.
• Added tests for rootless Docker configurations and custom socket paths.
• Created new documentation for rootless Docker setups and scenarios.
• Older Docker CE versions that bundled buildx with CLI will still respect the installDockerBuildx: false setting
  Modern Docker CE versions with separate packages work as expected
• Cleanup runs after installation so it can properly detect and remove bundled buildx files
• Added explanatory comments for future maintainers

Key Points

1. *socketPath option: Configures where the feature expects the socket inside the container
2. Mount source: Must match your host's actual Docker socket location
3. Mount target: Must match the socketPath option value
4. XDG_RUNTIME_DIR: Usually /run/user/{uid} for rootless Docker

Test Scenarios

The test scenarios demonstrate:

• rootless_docker_socket: Standard rootless configuration

• root_docker_socket: Standard root Docker (for comparison)

• Checklist
  Changes works as expected for both root and rootless docker environments.

[Kaniska (v-Kaniska244)]

Hi sireeshajonnalagadda

I have left few comments. Please get back in case of any issues.

[Abdurrahmaan Iqbal (abdurriq)]

Implementation LGTM, some test changes requested.