Ensure OIDC properly logs out

[NHAS]

Currently, wag only ends its current session but not the session on the identity provider. This causes a very confusing loop for some users where hitting the logout button immediately redirects them to being logged in again.

This can be fixed in two ways:

1. Add a "Sign in with SSO" button
2. Redirect the user to the o.provider.GetEndSessionEndpoint() URL to signout the session at the IDP

For 2. I just want to make sure we dont unauthorise a users IDP session, or are at least given the option to only end Wags session. Just so this doesnt become frustrating for people.

@muff10
@krage3x

[krage3x]

I'm currently working on this and have made some progress. If you need this done faster and the current progress is enough for you, I'm happy to share the code I've been working on so far, so you can finish it earlier if needed.

[NHAS]

I'm not going to be able to work on this for a bit due to other life commitments. Feel free to just work on it and open a pr when you feel it's ready and I'll give it a review