tt multiinstance applications

[p7nov]

Epic: Document TT CLI
Related dev page: tarantool/tt#7

Product: Tarantool CLI
Since: 2.10
Audience/target: dev, admin
Root document: https://github.com/tarantool/tt#working-with-a-set-of-instances
SME: @ 0x501D

Details

Update descriptions of tt connect/start/stop/status to describe working with multiinstance applications.
Add a new page for tt clean.
All details are in the tt readme