a8n: Send campaigns count in usage pings

Created by: mrnugget

Fixes #7711 - This adds the total number of Automation campaigns in the database to the update ping.

This is just one number by design, since for now we only want to capture the number of campaigns per customer.

That's also why I simply defined one function in this package that queries the database directly. instead of using the a8n.Store. Because that would require moving the Store out of the enterprise/internal/a8n into the internal/a8n package. So I went for this tradeoff (duplicate mention of campaigns table here and in the store code).

What do you think?