[ZEPPELIN-6487] Update the deprecated pypi.python.org URL in the build docs

[soheetech]

What is this PR for?

This PR updates the deprecated pypi.python.org host to the active distribution file host files.pythonhosted.org in docs/setup/basics/how_to_build.md.
It also synchronizes the documented python.py4j.version (0.10.7) and python.py4j.repo.folder path with the project's actual build configuration in python/pom.xml, ensuring that the composed Py4J package download URL resolves correctly.

What type of PR is it?

Documentation

Todos

• - Replace deprecated pypi.python.org host with files.pythonhosted.org
• - Sync python.py4j.version and repo folder path with project build settings
• - Verify composed download URL produces HTTP 200

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-6487

How should this be tested?

1. Check docs/setup/basics/how_to_build.md in the "Py4J package" section.
2. Confirm the composed URL ${pypi.repo.url}${python.py4j.repo.folder}py4j-${python.py4j.version}.zip constructs: https://files.pythonhosted.org/packages/dd/03/d83f659f045d819fc7550dd472b3831fe8c8fa7204c6428270a46a4a5ab9/py4j-0.10.7.zip
3. Verify the URL returns HTTP 200 via curl -I:

   curl -I [https://files.pythonhosted.org/packages/dd/03/d83f659f045d819fc7550dd472b3831fe8c8fa7204c6428270a46a4a5ab9/py4j-0.10.7.zip](https://files.pythonhosted.org/packages/dd/03/d83f659f045d819fc7550dd472b3831fe8c8fa7204c6428270a46a4a5ab9/py4j-0.10.7.zip)

4. Run git diff --check to ensure no whitespace errors.

Screenshots (if appropriate)

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No (this PR updates documentation itself)

[voidmatcha]

LGTM 👍 This addresses ZEPPELIN-6487. I opened https://issues.apache.org/jira/browse/ZEPPELIN-6725 to remove the unused Py4J download settings from the guide as a separate follow-up.

[tbonelee]

Merged into master