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

docs/docs/install/config-file.md

@@ -193,6 +193,7 @@ The default configuration looks like this:
     "defaultStorageQuota": null,
     "enabled": false,
     "issuerUrl": "",
+    "endSessionEndpoint": "",
     "mobileOverrideEnabled": false,
     "mobileRedirectUri": "",
     "profileSigningAlgorithm": "none",