Define SSOT for time periods available in Usage Ping

Background

During review of !48778 (merged) at !48778 (comment 492017304) @mkozono raised very good question around, what happened if time_span encountered does not match expected one. That concern leaded to discover that there is no single source of truth (SSOT) that clearly defines that time periods used at Usage Pings are predefined.

Problem was discussed again by @a_akgun question in the review of !52784 (comment 500874298) pointed lack of well defined SSOT for time ranges in UsageData metrics. To avoid inaccurate results we should extract dates into SSOT

Goal

We should have all available time ranges of metrics collection defined in the single location, and shared among all places that instruments, or collect metrics. So far only last_28_days has been implemented that way