support other sources

support other sources

https://github.com/apache/incubator-wayang/blob/388cce9f8955c4c2e8df7b4094e4a7416340754f/wayang-api/wayang-api-sql/src/main/java/org/apache/wayang/api/sql/calcite/converter/WayangTableScanVisitor.java#L29

```java

package org.apache.wayang.api.sql.calcite.converter;

import org.apache.wayang.api.sql.calcite.rel.WayangTableScan;
import org.apache.wayang.core.plan.wayangplan.Operator;
import org.apache.wayang.postgres.operators.PostgresTableSource;

import java.util.List;

//TODO: create tablesource with column types
//TODO: support other sources
public class WayangTableScanVisitor extends WayangRelNodeVisitor {
WayangTableScanVisitor(WayangRelConverter wayangRelConverter) {
super(wayangRelConverter);

```

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