Add recent new howto topics to Howto index

What does this Merge Request do?

Until we have automation: #1176, fill out the Howto index with some recent additions, and improves some old ones.

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.