feat: add PEP 621 config only (#1031)

* feat: add PEP 621 config only

* Apply suggestions from code review

Co-authored-by: Brett Cannon <brett@python.org>

* fix: minor fixes

* refactor: include (future) setuptools

* fix: stripping a bit more

* fix: one more change as requested

* chore: include hatch and experimental setuptools

* fix: more positive setuptools mention

* chore: use setuptools 61, mark experimental

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* refactor: place hatchling first

* Apply suggestions from code review

Co-authored-by: Brett Cannon <brett@python.org>

* Update source/tutorials/packaging-projects.rst

Co-authored-by: Ofek Lev <ofekmeister@gmail.com>

* refactor: addressing review feedback

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* refactor: reorder backends and add recommendation

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* Edit for accuracy/simplicity, add TODOs

* Refer to distributions instead of archives

* Fix typo, add TODO

* Fix typos

* Rework build backend section

* refactor: match package name

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* Update source/tutorials/packaging-projects.rst

Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>

* fix: linkcheck, Py 3.7+, and periods are valid

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* Make changes based on discussion thread

* Remove placeholder link

* Minor copy-edits

Co-authored-by: Brett Cannon <brett@python.org>
Co-authored-by: Ofek Lev <ofekmeister@gmail.com>
Co-authored-by: Brian Rutledge <brian@bhrutledge.com>
Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>