Allows `alias` option on route definitions

## Summary

Vue router allows for `alias` property to assign an alias path the component can be accessed on.
It is currently not possible to pass this to `createPage` an error is thrown stating:

```
"alias" is not allowed
```

### Basic example

https://router.vuejs.org/guide/essentials/redirect-and-alias.html#alias

### Motivation

My immediate use case was to rehydrate the router on the client under a different URL (not a different base url but an entirely different url)

For example:

`/home` & `/homebase`

Start by locating createPage and the route-option validation that rejects `alias`, then compare the accepted options with Vue Router's alias behavior. The work is done when route definitions can pass an `alias` path without the current validation error and the `/home` and `/homebase` example can resolve the component as described.

Written by the indexing model from the issue text.