Allow to preselect an Auth0 "connection" via staticwebapp.config.json

**Is your feature request related to a problem? Please describe.**

In the `staticwebapp.config.json` file I configured Auth0 as a custom authentication provider within the `auth` section.

**My goal/problem**: I want to preselect a specific "connection" from several identity providers, but don't know how to configure this via the `staticwebapp.config.json` file.

In the Auth0 documentation the connection parameter is described in the [webAuth.authorize()](https://auth0.com/docs/libraries/auth0js#webauth-authorize-) section. So I need a way to configure this parameter in the `staticwebapp.config.json`.

Without this I cannot use the SWA built-in authentication mechanism at all which would be really frustrating.

**Describe the solution you'd like**

I'd like to configure the "connection" parameter (documented in Auth0's [webAuth.authorize()](https://auth0.com/docs/libraries/auth0js#webauth-authorize-) method) via the `staticwebapp.config.json` file.

**Describe alternatives you've considered**

I could integrate the Auth0 JS library and set it all up in the SPA frontend and in some other way to add it to my backend (Azure functions), but I'd rather like to configure the authentication by only using the `staticwebapp.config.json` file.