docs(examples): update Custom Token Exchange section with delegation, organization, and vendor params

[cschetan77]

Summary

Updates EXAMPLES.md section 12 (Custom Token Exchange) to document the new options added in #834.

• Delegation / impersonation — new subsection showing actor_token + actor_token_type usage and how to read the act claim from the response
• Organization-scoped exchange — new subsection showing the organization first-class option
• Vendor-specific parameters — updated to remove organization (now first-class) and clarify extra is for params like connection