Enable usage data FF unique_users_pushing_mr_ciconfigfile of PA

What does this MR do?

This MR enables the FF usage_data_o_pipeline_authoring_unique_users_pushing_mr_ciconfigfile by default.

• Feature issue: #287682 (closed)
• Introduced in: !54707 (merged)
• FF rollout issue: #322166 (closed)

It is enabled on GitLab.com => #322166 (comment 537356000)

Does this MR meet the acceptance criteria?

Conformity

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