[AIBundle] Simplify agent-as-tool configuration

[valtzu]

I'm proposing to simplify agent-as-tool (chain-in-chain) configuration.

Current situation

  tools:
    - service: ai.agent.my_agent
      name: my_agent
      description: My wonderful agent
      is_agent: true

The proposal

  tools:
    - agent: my_agent # This references the agent name and also serves as default tool name unless name is defined explicitly here
      description: My wonderful agent

[chr-hertel]

Great idea - and you're making Mr. Stark quite happy I guess :D

(Oskar was not a fan of my is_agent solution at all)

[OskarStark]

Yes 🙏 😃