Document dependent pages functionality

[scott1702]

Some CMS users have been uncertain as to what the "Dependent pages" tab is on pages in the CMS, mentioning that they couldn't find anything after searching through userhelp/cwp documentation.

[sachajudd]

cc @clarkepaul

[clarkepaul]

This wasn't a UX directed change, I think it got added along with file links but then file links got removed from the UI again. It does have a pretty straightforward description in the CMS about what it is but if there is no help text for it we can add some text for it.

Personally, I think the tab is too prominent in the UI it adds unnecessary clutter but I don't think we'll be changing this anytime soon. I think it would be better to have some sort of page summary. e.g. 2 internal links, 3 external links, 4 files used, page speed, ease of reading content and so on but that is way off.