Add count_distinct_user_id_from_create_ci_runner_by_authenticated_user

What does this MR do and why?

This MR adds a metric to the existing create_ci_runner internal event, so that we count distinct user IDs where property: authenticated_user.

References

• Instrument the creation of CI runners (!179876 - merged)
• Runner stage instrumentation audit (#554144 - closed)

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