refactor: use ejs templates for `vite.config.*` (#292)

refactor: use ejs templates for `vite.config.*` (#292)

The base template has a `vite.config.js.ejs` template file, which reads data from a corresponding `vite.config.js.data.mjs` file. The data file has a default export called `getData()`.
Other templates can also have data files that can be chained together so that they can modify the data fed into the template. They don't have to define the template again, though.

This fixes the issue mentioned in https://github.com/vuejs/create-vue/pull/257#issuecomment-1582022157

As we don't support plugins or extensions for this tool, I didn't choose to design the feature in an extensible way, but only considered ease of implementation and ease of modification.