feat: add Docker support (exec/run) for PHP CS Fixer

[jexme]

Adds optional Docker integration to run PHP CS Fixer inside containers using either docker exec (default) or docker run. Disabled by default to keep existing behavior unchanged.

What’s included

• New settings:
  • php-cs-fixer.docker.enable (boolean, default: false)
  • php-cs-fixer.docker.mode: "exec" | "run" (default: "exec")
  • php-cs-fixer.docker.command (e.g., "docker" or "podman")
  • php-cs-fixer.docker.image (for run)
  • php-cs-fixer.docker.container (for exec)
  • php-cs-fixer.docker.workspaceFolder
  • php-cs-fixer.docker.runExtraArgs / php-cs-fixer.docker.execExtraArgs
• Proper path mapping for config files and targets inside the container.
• Clear error messages for missing image/container/binary or docker CLI.

Backward compatibility

• Default settings keep Docker disabled. Existing workflows and behavior are unchanged.

the only thing is, I think the build will need to be restarted so that the new index.js appears

[Filipe07]

What is the status of this PR? Can we merge it?
My team have the same use case and this would be very useful