Assign Feature Flags To All Clients

Idempotently assign the given feature flags with value="true" to all active clients. Clients that already have a flag correctly assigned are skipped.

Body example::

{
    "feature_flag_ids": ["<uuid-1>", "<uuid-2>"],
    "dry_run": false
}

Set dry_run: true to preview what would be changed without writing to the database.