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/config.ts

@@ -104,6 +104,7 @@ export type SystemConfig = {
     defaultStorageQuota: number | null;
     enabled: boolean;
     issuerUrl: string;
+    endSessionEndpoint: string;
     mobileOverrideEnabled: boolean;
     mobileRedirectUri: string;
     prompt: string;
@@ -297,6 +298,7 @@ export const defaults = Object.freeze<SystemConfig>({
     defaultStorageQuota: null,
     enabled: false,
     issuerUrl: '',
+    endSessionEndpoint: '',
     mobileOverrideEnabled: false,
     mobileRedirectUri: '',
     prompt: '',