Add Copilot code review active user counts to Copilot usage metrics structs

[Tens1des]

The Copilot usage metrics API includes active and passive Copilot code review user counts on aggregated enterprise and organization reports, but go-github does not model them yet.

Docs: https://docs.github.com/en/copilot/reference/copilot-usage-metrics/copilot-usage-metrics

Missing fields on CopilotDailyMetrics:

• daily_active_copilot_code_review_users
• weekly_active_copilot_code_review_users
• monthly_active_copilot_code_review_users
• daily_passive_copilot_code_review_users
• weekly_passive_copilot_code_review_users
• monthly_passive_copilot_code_review_users

[Tens1des]

I'll take this)