How to document version updates that apply to multiple GitLab versions

Issue Description

gitlab!128038 added a workaround for an LDAP username config bug to update/index.md. The original draft had the bug notice in every version note affected.

After discussion with the TW team, we decided to limit the mention of the bug to the first version it occurs in rather than all the affected versions.

The main reason is that if someone was to go from, for example, 15.10 to 16.1, that they are implicitly upgrading the versions in between as well i.e. 15.11 and 16.0. Therefore the user should refer to the notes for all of the versions, and hopefully the bug information would not need to be repeated.

The original MR owner pushed back on this, citing that there was precedent in putting the bug notice in all versions affected, and that "(I)n terms of Support ticket deflection, adding the bug to all affected versions seems like a "low effort, high result" way of preventing customers getting caught out by it."

The discussion around which approach was correct highlighted a possible need to formalise this as a rule in the style guide.

Related to #843 (closed)