SPIKE: Create a list of sections in the docs that should be snippets

[snneji]

Context

To prevent duplication in docs we are implementing a snippets feature.

Tasks

1. Create a list of sections in the docs that should be snippets, where these should be reused / could reduce duplication.
2. Do one of the following:
   • Implement the snippets for the identified sections, OR
   • Make a new issue to implement snippets if the sections need heading offset and the offset feature has not yet been implemented in Implement new snippet plugin including offset functionality #4556.

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[snneji]

/lifecycle frozen

[abrennan89]

Added Concepts section and updated Revision, Garbage collection, serving and eventing snippets:

• Updating docs for Revisions #5156
• Create Concepts section #5155
• Update garbage collection docs #5183
  more to come

[abrennan89]

#5114 - the PDB part of this should be a snippet (note to self)

[abrennan89]

The docs keep growing so I think rather than trying to make this a list, let's just fix them as we go.