Epic: Establish Wagtail as a usable workflow on existing mozorg surfaces.

[alexgibson]

Description

Bedrock has a new Wagtail powered CMS back-end / database, but it is not yet powering any pages in production. The aim of this epic is to migrate one or more existing surfaces to be editable by the CMS, as well as establish the processes, guardrails, and workflows that need to be implemented in order to support CMS management in a safe, predictable manner.

Key results:

• Migrate one or more existing mozorg surfaces to Wagtail. Possible candidates include
  • Leadership page (updated regularly, en-US only).
  • VPN resource center (localized workflow).
• Implement user groups and permissions for editing, previewing, approving and publishing content.
• Implement content publishing approvals and workflow.
• Document workflows, processes and software-enforced “guard rails” for:
  • CMS users editing, and publishing content to existing CMS surfaces.
  • Developers creating new CMS editable content pages.
  • Developers updating models / templates for existing CMS editable content.

Epic will be broken down into individual issues below:

### Tasks
- [ ] https://github.com/mozilla/bedrock/issues/14798
- [ ] https://github.com/mozilla/bedrock/issues/14797
- [ ] https://github.com/mozilla/bedrock/issues/14801
- [x] Document how to migrate a page to the CMS
- [x] Add docs for running DB migrations and squashing migrations
- [ ] https://github.com/mozilla/bedrock/issues/14871
- [ ] https://github.com/mozilla/bedrock/issues/14829
- [ ] https://github.com/mozilla/bedrock/issues/14843
- [ ] https://github.com/mozilla/bedrock/issues/14859
- [ ] https://github.com/mozilla/bedrock/issues/14860
- [ ] Document scheduled publishing of pages (including making it explicit that the TZ in use is always PST)

[stevejalim]

Re moving the VPN Resource Center to Wagtail is that it'll be v interesting to see if the existing translation work is recognised as being valid and automatically reused, or if Wagtail will chunk the strings differently from Contentful. The latter would be a surprise, but let's see...