Update cext-trey-research-python sample

[garrytrinder]

This is a migrated sample from OfficeDev/Microsoft-365-Copilot-Samples and is a csharp variant of the da-trey-research sample.

Original author: Jegadeesh-MSFT

• Rename to da-trey-research-python
• Update README.md to reflect repo template
• Add assets folder and sample.json file
• Update Microsoft 365 Agent Toolkit files
• Update app manifest schema
• Update copilot extension references to declarative agent
• Add to samples list on repo README.md