[Chronik] Call SyncWithValidationInterfaceQueue in /broadcast-tx(s)
Summary:
Some tests occasionally fail because /broadcast-tx(s) returns before Chronik caught up.
Waiting using SyncWithValidationInterfaceQueue fixes this.
Test Plan: ninja check-functional
Reviewers: Fabien, #bitcoin_abc
Reviewed By: Fabien, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D15532