Chatbot: custom attach menu and attach actions in message bar

[merged dev issue](https://github.com/patternfly/chatbot/pull/789)
Add to figma:

- [ ] At start and at end "+" icon(new variant of message bar)
- [ ] adjust text in attach menu to match [demo](https://chatbot-pr-chatbot-789.surge.sh/extensions/chatbot/ui/#message-bar-with-custom-attach-menu-and-additional-actions)
- [ ] canvas label and model switcher in message bar


<img width="638" height="243" alt="Image" src="https://github.com/user-attachments/assets/37da0b60-0ae3-4261-97cb-de9cba08f39d" />
<img width="672" height="216" alt="Image" src="https://github.com/user-attachments/assets/bc9eb6a5-3758-4272-8411-aa0e5f0babf0" />
<img width="670" height="140" alt="Image" src="https://github.com/user-attachments/assets/5be7e6c0-442a-4fa6-a4a1-f98f45515ae7" />

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**Jira Issue:** [PF-3597](https://issues.redhat.com/browse/PF-3597)

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Chatbot: custom attach menu and attach actions in message bar #910

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Chatbot: custom attach menu and attach actions in message bar #910

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