Check front matter docs for missing contibutors, date created and wrong nav order #428

• I've checked the existing issues for this change

Describe the bug
Check front matter docs for missing contributors, date created and wrong nav order.

Many contributors are still missing from the front matter and also date created must be added for new content.
The nav order in the sidebar should be checked for inconsistencies and duplicate value.
This should be done before the migration to developer.wordpress.org