chore: use customizations/vscode/extensions instead of extensions property

[Marukome0743]

Description

Enhancements:

• Move VSCode extensions specification to the customizations.vscode.extensions section in .devcontainer/devcontainer.json

Motivation and Context

Property extensions is not allowed in the latest devcontainer.json.
Then use customizations/vscode/extensions instead.

Usage examples

{
  "name": "commitlint-dev",
  "dockerComposeFile": ["../docker-compose.yml"],
  "service": "commitlint",
  "workspaceFolder": "/root/repo",
  "shutdownAction": "stopCompose",
  "customizations": {
    "vscode": {
      "extensions": [
        "editorconfig.editorconfig",
        "esbenp.prettier-vscode",
        "ms-azuretools.vscode-docker",
        "ms-vsliveshare.vsliveshare-pack"
      ]
    }
  }
}

How Has This Been Tested?

I have tested it with GitHub Codespaces.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

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[escapedcat]

Thanks!