TCS: failover metrics

[lenkis]

Related dev. resources:

• Release card for TCS 0.24: https://jira.vk.team/browse/PRODUCTS-1359
• Dev ticket: https://jira.vk.team/browse/TNTP-108

Product: TCS
Since: 0.24
Audience/target: admins, end users (finops)
Root document: https://docs.d.tarantool.io/ru/column-store/doc/latest/
SME: @ Galiev-Ruslan

Details

Mostly probably will boil down to only 1 metric value, failover coordinator uptime.