multi: add a re-usable TxOptions type

Add a re-usable implementation of the sqldb.TxOptions interface and make
use of this in the various spots (invoices, batch and graph/db) where we
had previously defined individual implementations that were all doing
the same thing.

invoices/sql_migration_test.go

@@ -317,8 +317,8 @@ func testMigrateSingleInvoiceRapid(t *rapid.T, store *SQLStore, mpp bool,
 		invoices[hash] = invoice
 	}
 
-	var ops SQLInvoiceQueriesTxOptions
-	err := store.db.ExecTx(ctxb, &ops, func(tx SQLInvoiceQueries) error {
+	ops := sqldb.WriteTxOpt()
+	err := store.db.ExecTx(ctxb, ops, func(tx SQLInvoiceQueries) error {
 		for hash, invoice := range invoices {
 			err := MigrateSingleInvoice(ctxb, tx, invoice, hash)
 			require.NoError(t, err)