Add ability to control the number of levels shown in a table of contents

The Knowledge Base allows formatting of up to 6 heading levels. These will currently all show in a table of contents. This is too many

The table of contents becomes way too long where most people only need to see maybe a 2 level summary

Add a control to the table of contents to be able to select how many levels to show. For example, show 2 levels in the table of contents