Ability to instantiate infrastructure from shift.json itself

[pratishshr]

Description

Currently, infrastructure is only created when shift setup is run
Shift should be able to create Infrastructure from shift.json itself.

When shift setup is run, check if the current directory already consists of a shift.json file.
If it does, ask the user if he wants to use the existing shift.json config,
if yes, create infrastructure from the existing config,
if not, start the normal QnA process