Docs build passes despite internal links in migration guide

[DaveCTurner]

The migration guide docs are re-used in the stack-wide Install and Upgrade Guide which means we cannot use internal links there. I've fallen foul of this rule multiple times, most recently here. Could we fail the PR build on this misuse rather than relying on an eagle-eyed reviewer spotting the problem?

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[lcawl]

As soon as the appropriate files exist in the various repos, there's no reason we can't add those references in the Installation and Upgrade Guide. The docs build checks in individual PRs will then fail when inappropriate links are added. I've created elastic/stack-docs#1852 to update the files pulled in for 7.x branches. This is usually something we check as part of our docs release process, however, so we typically don't catch these too far in advance.

My hope is that the need for this repeated content will go away as we reorganize our content in the new documentation system.

[lockewritesdocs]

While valid, we're moving towards a new doc system, and will be investing less time and resources in patching the old one. I'll mark this issue as closed unless someone has the bandwidth to carry it forward.