Follow on patch for https://github.com/saltstack/salt/pull/18536

Hi
With this patch, now Salt-{1-3}.pdf have intended chapters in each pdf. Previously Salt-2.pdf and Slat-3.pdf have no TOC or chapters' content.

The know issue of this separation is that some of reference(in Slat-1.pdf) will not able to click and jump to destination(Salt-2.pdf).