Document Docker socket mount for Codespaces devcontainer

[Copilot]

Extracts the devcontainer configuration from PR #7423 and adds documentation for users who need Docker access within Codespaces.

Changes

• Added "Running Docker containers in Codespaces" subsection to doc/contribute/build_setup.rst
• Documents the required mounts configuration for devcontainer.json

Configuration

"mounts": [
  "source=/var/run/docker.sock,target=/var/run/docker.sock,type=bind"
]

Mounts the host Docker socket to enable running Docker commands within the Codespace environment.

Original prompt

Can you take #7423, extract the change it contains, and do a PR that adds a section to the build_setup part of the documentation to say "if you want to run docker containers in your codespace, here is how you need to modify the devcontainer config first".

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[Copilot]

Pull Request Overview

This PR adds documentation for running Docker containers within GitHub Codespaces by mounting the Docker socket. This enables developers to execute Docker commands from within their Codespace development environment.

• Adds a new section explaining how to configure Docker socket mounting in Codespaces
• Provides specific devcontainer configuration instructions with a JSON code example