- In tx_pool, add a column called `external_delete` that can be set to true
externally. Regularly, the coordinator will delete all pending txs with this
column set to true. The interval for this action is set via the new config
parameter `Coordinator.PurgeByExtDelInterval`.
- In tx_pool, add a column for the client ip that sent the transaction. The
api fills this value using the ClientIP method from gin.Context, which should
work even under a reverse-proxy.