`tt enable` command

**Product:** tt cli
**Since:** tt-ee 2.4.0
**Audience/target:** all
**Root document:** new page in https://www.tarantool.io/en/doc/latest/reference/tooling/tt_cli/commands/
**SME:** @ oleg-jukovec 

# Details

`tt enable`: create a symbolic link in 'instances_enabled' directory to a script or
an application directory.