Add „Hide already added devices“ badge to external integrations

In the original version of Gladys (with native integrations), it was possible to hide already added devices in the discovery tab.

Useful when you have many devices, but this feature has disappeared with external integrations.

I (Claude) am preparing a PR to restore this feature!

Edit: The PR: External integration Discovery: “Hide devices already added” toggle (GladysAssistant/Gladys#3375)