TCS: config validation to prohibit index_depth=0 for indexed columns

[lenkis]

Related dev. resources:

• TCS release cards: https://jira.vk.team/browse/PRODUCTS-682
• Dev ticket: https://jira.vk.team/browse/TNTP-2930

Product: TCS
Since: 0.28.1
Audience/target: admins, end users (finops)
Root document: https://www.tarantool.io/ru/column-store/doc/latest/
SME: @ ch3rrydrunk, @ Galiev-Ruslan

Details

Add info to config validation section + check if all index_depth occurrences in the doc strictly prohibit this scenario.

[lenkis]

closed with commit https://github.com/tarantool/tcs-doc/commit/74c1fccede3f525b4dec0a91498f2affed567f30