feat(server): support watch publicDir in dev

[liyincode]

Summary

support watch publicDir in dev
set watch: true, page will reload when watch file content changed.

    server: {
        publicDir: {
          watch: true,
        },
      },

Related Links

#1903

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[chenjiahan]

🎉🎉

[liyincode]

🎉🎉

WoW🤟