[SPARK-40012][PYTHON][DOCS] Make pyspark.sql.dataframe examples self-…

…contained

### What changes were proposed in this pull request?

This PR takes #37444 over with covering all examples in `pyspark.sql.dataframe`.

This PR proposes to improve the examples in `pyspark.sql.dataframe` by making each example self-contained with more realistic examples.

Closes #37444

### Why are the changes needed?

To make the documentation more readable and able to copy and paste directly in PySpark shell.

### Does this PR introduce _any_ user-facing change?

Yes, Documentation changes only

### How was this patch tested?

Manually ran each examples.

Closes #37702 from HyukjinKwon/SPARK-40012.

Lead-authored-by: Hyukjin Kwon <[email protected]>
Co-authored-by: William Zijie <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>