Replace plone/generator-volto with Cookieplone

[stevepiercy]

Update all files that refer to plone/generator-volto with Cookieplone.

Also replace or remove cookiecutter-plone-starter and cookiecutter-zope-instance as needed.

See also:

• Update cookie* references to current Volto 18.0.0-alpha.43 release documentation#1706
• Update Glossary with modern cookiecutters documentation#1705

[davisagli]

Cookieplone is designed for use with Volto 18.

For earlier Volto, it's still recommended to use plone/generator-volto (if you need just a frontend) or cookiecutter-plone-starter (it also uses plone/generator-volto, but generates a full project with frontend and backend).

cookiecutter-zope-instance is still relevant; it is used by both cookiecutter-plone-starter and cookieplone to create a Zope instance to run the backend.