Revise dialogue timeout handling

[Dacksus]

To allow dialogues being picked up again even after agent restart, dialogue history is persisted in a json file, which needs to be removed at some point. Since proper conclusion of a dialogue can't be guaranteed, there currently is a local timeout, after which a dialogue is removed. There are several potential issues with that that need to be addressed:

• the timeout is currently not synced, i.e., both parties could have different timeouts without knowing why the other party is not responding anymore (after their local timeout expired)
• the timeout is not considered anywhere in the dialogue engine (e.g., asserting that it is not expired before sending another message), it would only inherently lead to failure as one side won't be able to recognize the session anymore