Enable connection testing for gh-copilot

[ewega]

Summary

The Copilot plugin supports \POST /plugins/gh-copilot/test\ for validating connection parameters before creation. The CLI should use this to catch bad tokens or missing permissions early.

Changes

• Set \SupportsTest: true\ on the \gh-copilot\ entry in \connectionRegistry\
• Add \Organization\ and \Enterprise\ fields to \ConnectionTestRequest\ struct
• Pass org/enterprise in \BuildTestRequest\ for plugins that need them

Acceptance Criteria

• \gh devlake configure connections --plugin gh-copilot\ tests connection before creating
• Bad token shows failure message without creating the connection
• Missing PAT scopes (\manage_billing:copilot) are caught at test time
• Unit test for \BuildTestRequest\ verifies org/enterprise are included for Copilot but not GitHub

[ewega]

Implemented in the enterprise support branch. Scope ID fix, connection testing, rate limit alignment, and Connection struct enrichment all shipped.