fix(auth): don't read the provider's userinfo endpoint by default

Cloudflare Access answers userinfo without a Content-Type, which the
OpenID Connect handler rejects ("Unknown response type"), so every
sign-in failed after the code exchange. The ID token already carries
sub and email; DorkNet:SignIn:UseUserInfoEndpoint turns the call back
on for providers that need it.

DorkNet.Server/Startup/ServiceCollectionExtensions.cs

@@ -484,7 +484,7 @@ public static class ServiceCollectionExtensions
                 o.Scope.Add(scope);
             o.SignInScheme = ExternalSignIn.ExternalScheme;
             o.CallbackPath = ExternalSignIn.CallbackPath;
-            o.GetClaimsFromUserInfoEndpoint = true;
+            o.GetClaimsFromUserInfoEndpoint = signIn.UseUserInfoEndpoint;
             o.MapInboundClaims = false;
             o.SaveTokens = false;
             o.CorrelationCookie.SecurePolicy = secure;