feat(example): search agent example

[Dacksus]

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This PR provides an example for how to implement a search agent to extend on the basic agentverse search functionality. The search agent will get a general list for agents potentially satisfying the search request from agentverse search engine and then verify additional agent specific attributes with each agent individually. This allows for example to search for all EV charging stations in a certain area (search engine) that are below a given price limit (search agent).

There are two implementations for the search agent: The async implementation uses the common message handler-based approach and potentially scales better. The sync implementation makes use of the new send_and_receive feature, which makes it easier to follow the code for people unfamiliar with asynchronous communication.