[FLINK-38806] Fix post-transform converters ineffective without projection or filter rules

[yuxiqian]

This closes FLINK-38806.

A post-transform converter will not work if neither projection nor filter rule is defined, as such transform definitions are ignored in TransformTranslator.

transform:
  - source-table: foo.bar
    converter-after-transform: SOFT_DELETE

Questionable code snippet:

// TransformTranslator.java

 for (TransformDef transform : transforms) {
-    if (transform.isValidProjection() || transform.isValidFilter()) {
         postTransformFunctionBuilder.addTransform(
                 transform.getSourceTable(),
                 transform.getProjection(),
                 transform.getFilter(),
                 transform.getPrimaryKeys(),
                 transform.getPartitionKeys(),
                 transform.getTableOptions(),
                 transform.getPostTransformConverter(),
                 supportedMetadataColumns);
     }
 }

[lvyanquan]

LGTM.