Notify only internally about the audit result for costs audit

[iuliag]

Is your feature request related to a problem? Please describe.
Notify only internally about the audit result for costs audit.

Describe the solution you'd like
Add a post-processor notifying only internally about the audit result.

Describe alternatives you've considered
Get costs via the API

Additional context
Costs audit is a global audit, scheduled weekly, by default disabled in the global configuration.
It is only enabled on dev, for ahrefs.com site.
#365