Unified Backups: Bootstrap `gitlab-unified-backup` tool

Proposal

Introduce a new tool to handle Simple back up procedures.

The new tool should be written as a CLI application and support --help or -h to inform the user of the supported commands and option flags.

It should also provide a version number information through --version.

This code should include initial RSpec test infrastructure to cover help and version use-cases, and be ready to be expanded later on for additional commands.