Add support for wait operation on the backup resource

[remyleone]

Description

I would like to have the option to wait on a "scw rdb backup" commands.

• backup create -w
• backup restore -w
• backup export -w

How this functionality would be exposed

References

Version

version 2.0.0-beta.4+dev
build-date unknown
go-version go1.14.4
git-branch unknown
git-commit unknown
go-arch amd64
go-os darwin