feat: support config injectCSS.insertAt

[mzl980425]

增加配置里 injectCSS 的类型 { insertAt: 'top' } 可以控制注入 CSS 注入到

的顶部或底部

参考：https://github.com/egoist/rollup-plugin-postcss#inject

[codecov[bot]]

Codecov Report

Merging #459 (1ad1ef7) into master (4c24f53) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #459   +/-   ##
=======================================
  Coverage   74.20%   74.20%           
=======================================
  Files          17       17           
  Lines         535      535           
  Branches      194      194           
=======================================
  Hits          397      397           
  Misses        137      137           
  Partials        1        1           

Impacted Files	Coverage Δ
packages/father-build/src/schema.ts	100.00% <ø> (ø)

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[PeachScript]

感谢贡献，father 4 已发布，旧版本不再迭代，PR closed