(Continuation of the app eventing rock, as started in COST-2685)

Let's add 2 new notifications:

• E-mail/Splunk: “your data export is ready”. Depends on COST-2223.

• (Daily/weekly e-mail) Screenshot and table with today’s cost explorer snapshot. Since we cannot send cost data over e-mail due to privacy and data protection, we should send a URL pointing back to a c.r.c-hosted report (e. g. PDF). Better done after CIAM is ready, to avoid c.r.c logins.