coveragedb: it is growing too fast

[tarasmadan]

Describe the bug
~700 sessions cost ~70GB.
1 session is a day, month or quarter aggregation.
The main contributor are the day coverage numbers.

Every namespace will generate 365 (days) + 12 (months) + 4 (quarters) sessions annually.

Expected behavior
I'd like it to grow much slower.
There are a few options (will touch days only):

1. Stop collecting numbers for days. Focus on months and quarters.
2. Remove line coverage data for old records. Line coverage costs a lot.
3. Remove old day coverage sessions. For example, store day coverage for the last month only.

Option 3 looks the best to me.
Every namespace will generate 12 + 4 sessions annually.