Changes

PR #1936 by ksylvan: New Vendor: Microsoft Copilot

• Add Microsoft 365 Copilot integration as a new AI vendor with OAuth2 authentication for delegated user permissions
• Enable querying of Microsoft 365 data including emails, documents, and chats with both synchronous and streaming response support
• Provide comprehensive setup instructions for Azure AD app registration and detail licensing, technical, and permission requirements
• Add troubleshooting steps for common authentication and API errors with current API limitations documentation
• Fix SendStream interface to use domain.StreamUpdate instead of chan string to match current Vendor interface requirements