Preliminary docs tidy for 2026.3 (#20745)
Summary of the issue:
We started performing rough grouping of changelog items around 2023.
Turning these subgroupings into subheadings would help with navigation.
Performing the review/update for the changelog for each release involves shuffling and often indenting items.
This makes it hard to review.
We could consider adding regular subheadings to our template when creating each new releases changelog sections.
This would make many changelog entries ordered from when they are first merged, making the beta docs review simpler.
Description of user facing changes:
Restructure changelog sections
