Multiple SWA can't be on the same domain due since root endpoint can't be changed

**Multiple SWA can't be on the same domain due since root endpoint can't be changed**

TLDR: No possibility to serve application-x.azurestaticapps.net/.auth/* under application-x.azurestaticapps.net/\/.auth/* which leads to only one SWA being able to be served under one domain.

The easiest way to describe this is with an example:

Assume you have a domain example.com where we serve two applications: example.com/x and example.com/y. The proxy is done with an Application Gateway, so /x* goes to application-x.azurestaticapps.net and /y* goes to application-y.azurestaticapps.net, with header X-FORWARDED-FOR and X-ORIGINAL-HOST set by the proxy.

One solution is to serve the static files from a subdirectory _x_ and _y_ for each app. This would be fine, if you don't need authentication.

The authencation routes are served under application-x.azurestaticapps.net/.auth/*, and when behind the proxy this url becomes example.com/.auth which does not match any of our defined routes. Therefore the need to move the default /.auth files to /x/.auth becomes apparent.

**To Reproduce**
Steps to reproduce the behavior:
1. Create a SWA where the root is on a different page than /, e.g. application-x.azurestaticapps.net/app-x/
2. Have a proxy for example.com that answers on the route example.com/app-x and forwards to application-x.azurestaticapps.net/app-x/ with rewritten host.
3. Try to login: example.com/app-x/login

```json
{
"trailingSlash": "auto",
"routes": [
{
"route": "/app-x/login",
"rewrite": "/.auth/login/github"
},
{
"route": "/app-x/profile*",
"allowedRoles": ["authenticated"]
}
],
"responseOverrides": {
"401": {
"redirect": "/app-x/login",
"statusCode": 302
}
}
}
```

**Expected behavior**
Expected behavior is that more than one SWA can be created on the same domain, while supporting authentication.