Add statistics by all subscriptions

[Dankoy]

Is your feature request related to a problem? Please describe.
User can request stats by his subscriptions. For example how many coubs bot generated for his subs (monthly, yearly). Bot could aggregate this info and reply with amount of coubs for each sub for each year/month.

Possible to request only selected month or year.

Describe the solution you'd like
Add controller, service and repository methods to support statistics using sent_coubs_registry table.

Describe alternatives you've considered
None

Additional context
None