feat: command to list pages that use each template

[wesleyboar]

Overview

Add a command that lists all pages using each template in the CMS, along with their full URLs.

Related

• help admins locate pages using Texascale deprecated templates
• help admins refactor or test page templates

Changes

• adds management command
• documents new command
• improves documentation for management commands

Testing

0. (if you have no instance) make setup
1. make start
2. docker exec -it core_cms sh -c "python manage.py list_page_templates"
3. (optional) test with multisite
   ^{see feat: support multisite switch via domain name #873}

UI

docker exec -it core_cms sh -c "python manage.py list_page_templates"

TEMPLATE: "fullwidth.html"
PAGES:
- Home (https://localhost:8000/)
- Home (https://127.0.0.1:8000/)

TEMPLATE: "standard.html"
PAGES:
- Site 1 News (https://localhost:8000/news/)
- Site 2 News (https://127.0.0.1:8000/news/)
- Site 1 Page (https://localhost:8000/site-1-page/)

TEMPLATE: INHERIT
PAGES:
- Site 2 Page (https://127.0.0.1:8000/site-2-page/)
- Remote Site 1 News (https://127.0.0.1:8000/remote-site-1-news/)