Update default vite options for Vite v3

[vivgui]

It seems Vite v3 deprecated string values for server.middlewareMode, it's a boolean now. The config value should be true now.

Also, we need to add appType as a shared config, the value should be custom according to the docs.

Let me know if you want me to amend anything.

[zachleat]

Thank you!

[wommy]

add appType: "custom" in the readme?

and can we get version bump