[6.8 HelpHub]: update changelogs for bundled themes

[carolinan]

(previously: #1798, #1031, #1275, #1517, #1654)

All the bundled themes need to update their changelogs when they are released.

The heading IDs/anchors should be in the pattern of #Version_1.2.

Note: the full log is not available at this time, this task can be completed at the time of the final release candidate.

[github-actions]

Heads up @kafleg @carolinan @TeBenachi - the "themes" label was applied to this issue.

[github-actions]

Heads up @WordPress/docs-issues-coordinators, we have a new issue open. Time to use 'em labels.