Linking release reference and worked examples

[pindec]

It would be helpful for people reading the release reference to link to relevant worked examples, just as links are given to relevant extensions.

For example, in the parties reference, the details field notes that extensions can provide detailed classification of parties, and the party details extensions are linked. It would also be helpful to link to the organization classifications worked example.

[jpmckinney]

We can create a simple Sphinx extension, where we add either Markdown frontmatter or a simple directive on the worked example, and then list the marked pages in the reference section.

Possible implementation inspiration is the example todolist directive: https://www.sphinx-doc.org/en/master/development/tutorials/todo.html

[duncandewhurst]

At the same time we can make the changes suggested in #1434 (comment):

...we want all content except the extensions list above the jsonschema directive, as otherwise it's easy to miss.)

I think we might start using a simpler format of "seealso ... How to [do X]" when linking to guidance.