## What changes were proposed in this pull request?

Add a non-intrusive button for python API documentation, which will remove ">>>" prompts and outputs of code - for easier copying of code.

For example: The below code-snippet in the document is difficult to copy due to ">>>" prompts
```
>>> l = [('Alice', 1)]
>>> spark.createDataFrame(l).collect()
[Row(_1='Alice', _2=1)]

```
Becomes this - After the copybutton in the corner of of code-block is pressed - which is easier to copy
```
l = [('Alice', 1)]
spark.createDataFrame(l).collect()
```

![image](https://user-images.githubusercontent.com/9406431/56715817-560c3600-6756-11e9-8bae-58a3d2d57df3.png

)

## File changes
Made changes to python/docs/conf.py and copybutton.js - thus only modifying sphinx frontend and no changes were made to the documentation itself- Build process for documentation remains the same.

copybutton.js -> This JS snippet was taken from the official python.org documentation site.

## How was this patch tested?
NA

Closes #24456 from sangramga/copybutton.

Authored-by: sangramga <sangramga@gmail.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>