A tag is required to reuse Elasticsearch breaking changes in the Stack
Guide. To display properly, the breaking changes must use external
links rather than xrefs.
This PR correctly places those tags for reuse. It also replaces
several xrefs with external links for reuse.
This is related to #36652. There are a number of transport settings that
were deprecated and replaced with new versions in 7.x. This commit
removes them from 8.0.