[MINOR][DOCS] Fix the Binder link to point the quickstart notebook correctly

[HyukjinKwon]

What changes were proposed in this pull request?

This PR fixes the link of Binder in Quickstart notebook and documentation.

From:

https://mybinder.org/v2/gh/databricks/apache/master?filepath=python%2Fdocs%2Fsource%2Fgetting_started%2Fquickstart.ipynb

To:

https://mybinder.org/v2/gh/apache/spark/master?filepath=python%2Fdocs%2Fsource%2Fgetting_started%2Fquickstart.ipynb

This link is the same as the one in RST files:

spark/python/docs/source/conf.py

Line 57 in b541030

.. _binder: https://mybinder.org/v2/gh/apache/spark/{0}?filepath=python%2Fdocs%2Fsource%2Fgetting_started%2Fquickstart.ipynb

Why are the changes needed?

The link was wrong, and points out non-existent file and repo.

Does this PR introduce any user-facing change?

Yes, it will fixes the link so users can correctly try Binder.

How was this patch tested?

Manually tested by building the documentation.

[HyukjinKwon]

Let me just merge this. I am 100% sure this is correct fix, and this is doc-only.

[SparkQA]

Test build #128096 has finished for PR 29597 at commit 3f2ce89.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.