feat(amazonq): feature flag for / agents migration to agentic chat

[Randall-Jiang]

Notes:

• Migrating the /Agents(/dev, /doc and /test) to Q Agentic chat experience.
• This does not disturb other /agents like /review and /transform.

TODO:

• Remove implementation code for above /agents from the VSC repository in followup PR's.

---

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[github-actions]

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