Add Integration credentials are saved correctly again

Bug Fixes

• Integrations: credentials entered in the Add Integration wizard (API keys, passwords and bearer tokens for HTTP-, MQTT-, SMTP- and Google Home-based integrations) are saved correctly again. A credential-hardening change in August had silently dropped them: the wizard reported success, but the connection was left with an empty credential, so for example Google TTS returned 403 on every request and AlAdhan's spoken reminders stayed silent. A credential write that is now rejected shows up in the log instead of looking like success. To pick up the fix on an existing node, update the platform first, then update the HTTP Service, MQTT Service, SMTP Service and Voice Assistant Service extensions from the Extensions app, and re-run Add Integration (or re-enter the credential) for any integration set up while this defect was live.