Tie the versions in the docs to those defined in spring-boot-dependencies

[wilkinsona]

We sometimes reference versions in the documentation that should match those defined in spring-boot-dependencies but it's a manual process to keep them in sync. We should see if there's a way to keep them in sync automatically. One possibility would be a custom Asciidoctor extension that exposes all of the version properties from spring-boot-dependencies as Asciidoctor attributes that could then be referenced, for example {{spring.version}}.

[philwebb]

We already set some so it should be pretty easy to add the ones we're missing.

[snicoll]

Closing in favour of PR #10774

[snicoll]

Oops that one is more general purpose, reopening