DOC Update syntax for callout blocks

IMPORTANT

This should not be merged until all of the associated PRs have all been approved. Only merge when all of the PRs are ready to go, to minimise the amount of time spent with broken callout blocks.

Description

Converts all of the legacy callout blocks to the new syntax. Note that we're not doing CMS 3.

There is a separate PR for CMS 4. Lots of the changes will be the same, but there's been enough change between majors that a direct merge up will be a pain in the butt, so I've done two separate PRs. Once they're both merged the merge-up process will literally be to throw away the differences and keep the CMS 5 copy.

Note that most of the callout blocks will be converted as per https://github.com/silverstripe/doc.silverstripe.org/issues/282#issuecomment-1915939874 - but there are some which were intentionally changed. I will note those with comments. If I haven't added a comment on something that has been converted differently than that table suggests, assume I messed up.

Issues

https://github.com/silverstripe/doc.silverstripe.org/issues/282

Pull request checklist

[x] The target branch is correct
- See branches and commit messages
[x] All commits are relevant to the purpose of the PR (e.g. no TODO comments, unrelated rewording/restructuring, or arbitrary changes)
- Small amounts of additional changes are usually okay, but if it makes it hard to concentrate on the relevant changes, ask for the unrelated changes to be reverted, and submitted as a separate PR.
[x] The commit messages follow our commit message guidelines
[x] The PR follows our contribution guidelines
[x] The changes follow our writing style guide
[x] Code examples follow our coding conventions
[x] CI is green

silverstripe / developer-docs