feat: weekly digest

[raquelmsmith]

Problem

I'd like to start letting people know what is happening in their posthog org/data every week. This is a first stab at that.

Changes

On mondays, gathers up a bunch of things that have happened in a project, like new feature flags created or surveys launched, and sends and event to posthog with that info. The event will be consumed by customer.io and an email sent out with the deets.

Todo:

• Remove this from the usage reports task and make it its own thing, as I realized later that I didn't actually need much of the foundation that the usage reports provided for this
• Add survey response data

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Does this work well for both Cloud and self-hosted?

How did you test this code?

Added a test, but need to move it when I abstract this out