feat(cli-service): allow override from option in pages config

[yoyo930021]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Underlying tools
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

Other information:
By example:
I have https://example.com, and have two version pages for mobile, desktop.

1. When type https://example.com, user go to a redirect page for screen size.
2. When type https://example.com/d, user go to a desktop page.
3. When type https://example.com/m, user go to a mobile page.
4. When type https://example.com/m/, user go to a mobile page.
5. When type https://example.com/message, user go to a redirect page for screen size.

Now it's impossible to meet all the conditions.

// vue.config.js
module.exports = {
  pages: {
    index: 'src/entry.ts',
    m: 'src/mobile/main.ts',
    d: 'src/desktop/main.ts'
  }
}

The fifth condition is not met when this config, user will go to a mobile page.