Regenerate PySpark API documentation for Spark 3.2.1

[xinrong-meng]

This PR regenerates PySpark API documentation for Spark 3.2.1.

Specifically, files under https://github.com/apache/spark-website/tree/asf-site/site/docs/3.2.1/api/python have been updated.

Currently, API of pandas API on Spark 3.2.1 are not associated with links, for example, API under https://spark.apache.org/docs/latest/api/python/reference/pyspark.pandas/series.html. So we wanted to regenerate it with correct dependencies.

How it gets updated:

• Generated docs under spark/python/doc against v3.2.1 Spark
• Copy generated files from spark/python/docs/build/html to spark-website/site/docs/3.2.1/api/python.

[srowen]

Out of curiosity what creates all the changes - is it just formatting or any substantive change?

[dongjoon-hyun]

This is wrong, isn't it? @xinrong-databricks

- <title>abc &#8212; PySpark 3.2.1 documentation</title>
+ <title>abc &#8212; PySpark master documentation</title>

cc @HyukjinKwon and @gengliangwang

[HyukjinKwon]

We should regenerate the docs by setting GIT_HASH and RELEASE_VERSION environments properly (see https://github.com/apache/spark/blob/master/python/docs/source/conf.py). BTW, I wonder why this failed to generate the docs this time .. I fixed it here apache/spark@03750c0

[gengliangwang]

Out of curiosity what creates all the changes - is it just formatting or any substantive change?

Same question here.
As many committers are watching this repo closely, @xinrong-databricks it would be great if you provide a summary of the changes in the PR description.

[xinrong-meng]

Sorry for the confusion. I added PR descriptions. Let me know if there are any questions.

FYI @HyukjinKwon @gengliangwang @srowen @dongjoon-hyun

[srowen]

It's hard to evaluate by looking at the diff but if it was merely regenerated from the 3.2.1 release to fix rendering of links, that seems OK

[HyukjinKwon]

Merged.