EPIC Review CMS5 doc for truthfulness

[maxime-rainville]

This was initially planned as a single card, but it turned out to be a bit toot much to chew in one go.

Acceptance criteria

• All CMS 3 and CMS 4 examples are removed/updated for CMS 5 doc
• CMS 5 doc is reviewed with a focus on area with substantial change
  • including validate all code examples still work

SCOPE

The primary purpose of this PR is to ensure that:

• code examples actually work in CMS 5
• written documentation is factually correct

It is okay to also augment the existing documentation to make it clearer or to add information you feel is missing, but don't focus on that.

It is also okay to updated code examples or written documentation to better reflect best practices - but that is not the main purpose of this PR. Don't explicitly look for it, but it's okay to fix it where you happen to notice it, if you want to.

Peer review should not suggest changes which focus on best practices, grammatical/spelling problems, or unclear language except where the content they're making the suggestion for is new in the PR. There will be separate best-practices and grammar/spelling reviews of the docs as a whole following this work.

EXPLICITLY OUT OF SCOPE

• Lessons (references to lesson will be removed)
• Not having namespaces (unless adding these is necessary for code to be clear or correct)
• Userhelp docs
• Docs not following best practices, but still factually correct (except where the practice being promoted is so bad it could introduce security issues - I saw some of those lingering around)
• Bad formatting