feat: support extra less options in dev and build mode

[focus7eleven]

{
  extraLessOptions: {
    modifyVars: {
      'primary-color': 'red',
       // or
      'hack': `true; @import "your-less-file-path.less";`, // Override with less file
    }
  }
}

[sorrycc]

已经有了 lessInBabelMode，配置项用 lessInRollupMode 吧，然后加个用了 modifyVars 的用例。

[focus7eleven]

updated

[sorrycc]

• father-build@1.11.0
• father@2.21.0