Finish pinning system rewrite (#8934)

* add oldest pyproject.toml file that works

* make single oldest_constraints.txt file

* remove unused merge_requirements.py

* remove unused import

* make conditional right

* simplify pip_install.py

* fix typo

* bump min dns-lexicon dependency

* fix zope import warning

* pin back wheel

* refactor pinning script

* Add oldest script.

* add pip comment

* add pipstrap extra

* simplify pinning scripts

* remove pipstrap extra

* update contributing

* Add design doc

* Update tools/pinning/DESIGN.md

Co-authored-by: ohemorange <erica@eff.org>

* Update tools/pinning/DESIGN.md

Co-authored-by: ohemorange <erica@eff.org>

* Update tools/pinning/DESIGN.md

Co-authored-by: ohemorange <erica@eff.org>

* Update tools/pinning/DESIGN.md

Co-authored-by: ohemorange <erica@eff.org>

* rename normal to current

* no dummies

* script improvements

* mention need to update setup.py

* try and clarify poetry behavior

* tweak section title

Co-authored-by: ohemorange <erica@eff.org>

certbot-dns-cloudxns/setup.py

@@ -7,7 +7,7 @@ from setuptools import setup
 version = '1.18.0.dev0'
 
 install_requires = [
-    'dns-lexicon>=3.1.0',  # Changed `rtype` parameter name
+    'dns-lexicon>=3.2.1',
     'setuptools>=39.0.1',
     'zope.interface',
 ]