public Jdbi setTransactionHandler(TransactionHandler handler) {
        Objects.requireNonNull(handler, "null transaction handler");
        this.transactionhandler.set(handler);
        return this;
    }
Specify the TransactionHandler instance to use. This allows overriding
transaction semantics, or mapping into different transaction
management systems.
<p>
The default version uses local transactions on the database Connection
instances obtained.
</p>

@param handler The TransactionHandler to use for all Handle instances obtained
               from this Jdbi
@return this
core/src/main/java/org/jdbi/v3/core/Jdbi.java