Add newly approved backend pings

Created by: CristinaBirkel

For context: https://github.com/sourcegraph/sourcegraph/issues/27214

List of pings to add:

• # of dashboards on an instance by week
• Avg, max, min , std dev, median # of insights per dashboard
• # of organizations with a dashboard
• # of organizations on an instance total

We can break these into smaller or individual issues as needed.