feat(server): add OIDC logout URL override option (#27389)

* feat(server): add OIDC logout URL override option
- Added toggle and field consistent with existing mobile redirect URI override.
- Existing auto-discovery remains default.
- Update tests and docs for new feature.

* fix(server): changes from review for OIDC logout URL override
- Rename 'logoutUri' to 'endSessionEndpoint'
- Remove toggle, just use override if provided
- Moved field in settings UI

server/src/repositories/oauth.repository.ts

@@ -22,6 +22,7 @@ export type OAuthConfig = {
   clientId: string;
   clientSecret?: string;
   issuerUrl: string;
+  endSessionEndpoint: string;
   mobileOverrideEnabled: boolean;
   mobileRedirectUri: string;
   profileSigningAlgorithm: string;