add additional checks around whether a SafeTransaction is cancelled or waiting to be indexed

[evitree]

Discussed with @rmeissner offline

Add checks or work around for safe-app-sdk's getBySafeTxHash or Safe Transaction API's getTransaction endpoint to ensure that we have a way to tell whether a transaction was actually cancelled (invalidated nonce) or whether it is marked as cancelled temporarily (nonce transaction detected but transaction has not yet been indexed).

For now we have a work around to only accept cancelled transactions that have cleared a few minutes after it's last updated date.

[evitree]

related issue which was flagged: safe-global/safe-client-gateway#37