website: postgraphile.org: Version 4 docs sync up and refresh

[jemgillam]

Description

Here I finish the Version 4 docs, ready to take them off of graphile.org.

This can't be merged until #2309 is live as it links to versioned docs on build.graphile.org which aren't live yet.

This PR includes

• utilize :::note and similar boxes
• fixing tailing slashes in URLs
• styling for <tt> tag when links are incorrectly automatically picked up by docusaurus
• remove unneeded front matter
• improve use of headings - <h5> doesn't really work as an anchor or style
• table of contents autogeneration on the applicable guide pages
• some Americanization when I spotted it
• fixes to anchor links within a page
• add and fix images in documentation pages
• fixes to titles in the side bar
• • This is done by the side bar title being in the front matter, and the longer title displayed on the page being in a <h1>
• • This tidies up the side bar rather nicely, most items in the sidebar are a lot shorter and mirror what is on graphile.org 😊
• ... loads more I'm sure

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Latest commit: 4be747c

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