Fix for Home Assistant 2024.6.0

[ov1d1u]

Seems that agent_manager.async_get_agent_info() now returns ConfigEntry entry_ids instead of entity_ids, while ConversationAgentSelector works with entity_ids. This means that when we look for an agent name in agent_names, we will lookup using an entity_id in a dictionary with entry_id as keys, so it will fail. To make this worse, we don't have entry_ids for the default agents (or I couldn't find one), so we end up with mixed key types in the agent_names dictionary. This causes the issue described in #14.

This PR modifies _convert_agent_info_to_dict function to check if an agent has a registry_entry property. If it does, we get the entity_id from there and use that as a key. I'm not 100% confident that this is the proper fix for this issue, so I'm open to suggestions.