Allow URL routes other than root

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## Bug description

We've configured the backendUrl for the dev portal, after the deployment of the static website in storage account, we've noticed that the home url couldn't load the css files, and it's being constantly redirected to the base url of the portal instead of the backendUrl that we configured.

## Reproduction steps

1. Go to 'https://{{ baseUrl }}/portal-apim'
2. Open browser console
3. See error "404 Resource Not Found" https://{{ baseUrl }}/styles/theme.css

## Expected behavior

The beautiful portal site should be loaded with all wwwroot assets.

## Is your portal managed or self-hosted?

Self-hosted

## Release tag or commit SHA (if using self-hosted version)

[e.g., release tag `2.8.0`]


Start by reproducing the /portal-apim URL and inspecting the browser console and network requests for the missing /styles/theme.css asset. Trace how the configured backendUrl and base route are applied to navigation and wwwroot asset paths; done means the portal loads from the non-root route without redirecting assets to the base URL.

Written by the indexing model from the issue text.