feat: add vscode config for ESLint

[yoshi-pi]

Description

If the user picks ESLint, then suggest the ESLint .vscode extension, and add the settings.

settings.json

{
  "editor.codeActionsOnSave": {
    "source.fixAll": "explicit"
  }
}

extensions.json

{
  "recommendations": ["dbaeumer.vscode-eslint"]
}

Related Issue

#466

Notes for Reviewers

• Created template/config/eslint dedicated to ESLint's static settings, including .vscode/extensions.json and .vscode/settings.json.
• Removed the existing code for adding the ESLint extension.
• Added code to merge Prettier settings into settings.json instead of overwriting them.
• Enabled generation of ESLint and Prettier snapshots.