Make sanitizeTemplateItems recursively check submenus in templates

[siemiatj]

Fixes #7098

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Automated tests

npm run test -- --grep="menuUtil tests sanitizeTemplateItems checks submenus recursively"

[bsclifton]

Looks great, thanks for the contribution @siemiatj! 😄