OpenID Connect RP-Initiated Logout

**Is your feature request related to a problem? Please describe.**
At the moment, when using a Custom OIDC provider, logging out of the SWA via /.auth/logout does only end the session on SWA side, but not on the side of the identity provider. From what we understand, you support this behaviour just for Google and AAD.

To service our application we need to be able to end the session with the custom OIDC provider when initiating the logout via /.auth/logout

**Describe the solution you'd like**
Open ID Connect describes the OpenID Connect RP-Initiated Logout [here](https://openid.net/specs/openid-connect-rpinitiated-1_0.html), as part of [OpenID Connect Session Management](https://openid.net/specs/openid-connect-session-1_0.html). We would like to get this implemented.

**Describe alternatives you've considered**
Exposing the OIDC token s.t. we could write an Azure function to call the end session endpoint, which then in turn redirects to /.auth/logout to perform the logout an SWA side

**Additional context**
This is a make or break feature for use, as otherwise we cannot achieve the quality and security we want to provide with our application. Thank you for looking into this!