www/beautifulsoup: Convert build to use PEP 517 and rename to PyPI name

• Rename port to PyPI name according to Python policy
• Move build completely to PEP 517
• Take maintainership as agreed with wen

New name: www/beautifulsoup4

PR: 297837
Approved by: wen (maintainer via mail)
Differential Revision: https://reviews.freebsd.org/D59143