Support 'SHOW VITESS_MIGRATIONS' from inside a transaction

Signed-off-by: Shlomi Noach <2607934+shlomi-noach@users.noreply.github.com>

go/vt/vttablet/tabletserver/query_executor.go

@@ -203,7 +203,7 @@ func (qre *QueryExecutor) Execute() (reply *sqltypes.Result, err error) {
 	case p.PlanRevertMigration:
 		return qre.execRevertMigration()
 	case p.PlanShowMigrations:
-		return qre.execShowMigrations()
+		return qre.execShowMigrations(nil)
 	case p.PlanShowMigrationLogs:
 		return qre.execShowMigrationLogs()
 	case p.PlanShowThrottledApps:
@@ -308,6 +308,8 @@ func (qre *QueryExecutor) txConnExec(conn *StatefulConnection) (*sqltypes.Result
 		return qre.execLoad(conn)
 	case p.PlanCallProc:
 		return qre.execProc(conn)
+	case p.PlanShowMigrations:
+		return qre.execShowMigrations(conn)
 	}
 	return nil, vterrors.Errorf(vtrpcpb.Code_INTERNAL, "[BUG] %s unexpected plan type", qre.plan.PlanID.String())
 }
@@ -958,7 +960,7 @@ func (qre *QueryExecutor) execRevertMigration() (*sqltypes.Result, error) {
 	return qre.tsv.onlineDDLExecutor.SubmitMigration(qre.ctx, qre.plan.FullStmt)
 }
 
-func (qre *QueryExecutor) execShowMigrations() (*sqltypes.Result, error) {
+func (qre *QueryExecutor) execShowMigrations(conn *StatefulConnection) (*sqltypes.Result, error) {
 	if showStmt, ok := qre.plan.FullStmt.(*sqlparser.Show); ok {
 		return qre.tsv.onlineDDLExecutor.ShowMigrations(qre.ctx, showStmt)
 	}