fix(mirror): use correct statements on push (#8414)

# Which Problems Are Solved

The mirror command used the wrong position to filter for events if
different database technologies for source and destination were used.

# How the Problems Are Solved

The statements which diverge are stored on the client so that different
technologies can use different statements.

# Additional Context

- https://discord.com/channels/927474939156643850/1256396896243552347

internal/v2/eventstore/postgres/push_test.go

@@ -1297,7 +1297,10 @@ func Test_push(t *testing.T) {
 				t.Errorf("unexpected error in begin: %v", err)
 				t.FailNow()
 			}
-			err = push(context.Background(), tx, tt.args.reducer, tt.args.commands)
+			s := Storage{
+				pushPositionStmt: initPushStmt("postgres"),
+			}
+			err = s.push(context.Background(), tx, tt.args.reducer, tt.args.commands)
 			tt.want.assertErr(t, err)
 			dbMock.Assert(t)
 			if tt.args.reducer != nil {