appendRowGroup will loose pageIndex

Currently, 
org.apache.parquet.hadoop.ParquetFileWriter#appendFile(org.apache.parquet.io.InputFile) uses appendRowGroup method to concate parquet row group. However, appendRowGroup method **looses** column index.
```java

// code placeholder
  public void appendRowGroup(SeekableInputStream from, BlockMetaData rowGroup,
                             boolean dropColumns) throws IOException {
....
    // TODO: column/offset indexes are not copied
      // (it would require seeking to the end of the file for each row groups)
      currentColumnIndexes.add(null);
      currentOffsetIndexes.add(null);
}
```
 

Look forward to functionality that support append with page index.

**Reporter**: [GANHONGNAN](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=NathanKan)

_{**Note**: *This issue was originally created as [PARQUET-2340](https://issues.apache.org/jira/browse/PARQUET-2340). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Start in parquet-hadoop/src/main/java/org/apache/parquet/hadoop/ParquetFileWriter.java at appendFile(InputFile) and appendRowGroup. Trace how row-group column and offset indexes are represented and why the current method adds null entries. Review the surrounding writer logic and existing tests, then define completion as appended row groups retaining their page indexes.

Written by the indexing model from the issue text.