[Task]: Flush Text File Output

### What needs to happen?

Migration: https://issues.apache.org/jira/browse/HOP-2568

Add option to flush the output stream on a regular interval or just flush every few seconds by default.
For slow-arriving data it's annoying that nothing is shown in the output file until a certain size is reached.

### Issue Priority

Priority: 3

### Issue Component

Component: Transforms

The issue does not name files or tests; start by locating the Text File Output transform in the Java source and tracing how its output stream is written and closed. Determine how a configurable interval or default periodic flush should behave for slow-arriving data, then verify that output becomes visible before the stream reaches its size threshold.

Written by the indexing model from the issue text.