Synchronize plan prices

curl --request POST \
  --url https://api.cloud.flexprice.com/v1/plans/{id}/sync/subscriptions \
  --header 'x-api-key: <api-key>'

{
  "message": "<string>",
  "plan_id": "<string>",
  "plan_name": "<string>",
  "synchronization_summary": {
    "prices_added": 123,
    "prices_removed": 123,
    "prices_skipped": 123,
    "subscriptions_processed": 123
  }
}