Add support for fixed-width header images

Issue Summary

With the recently released changes to the page header (content topper), Confluence no longer offers a fixed-width option for cover images. (Relevant Community Post)

This feels like a feature gap because Confluence does offer fixed-width pages.

In other words, if I'm using a fixed-width page, I now have no option to have the cover image fit that width as well.

This is reproducible on Data Center: No

Steps to Reproduce

1. Create a page
2. Add a cover image

Expected Results

There is an option for me to keep the cover image from extending into the margins.

Actual Results

The cover image extends beyond the fixed-width content area and into the page margins.

Workaround

None