Serverless Stack

Hey guys, I have this command like others suggested, and works perfectly:
```"start": "AWS_PROFILE=development sst start --stage $USER"```
The problem is some of my developers has $USER like `name.surname` , then the expression is not valid to name the stage or stack.
Any suggestions?

<https://github.com/serverless-stack/serverless-stack/pull/772/files#diff-b03e7694ae8e959162f64102e74d522636620b8064a0b02eb61f4c71fb7800feR26>

It'll make it so if `--stage` is not passed in, the user is prompted to enter a personal stage name (suggests an option generated from their IAM credential)

Yeah we're creating a new folder called `.sst` (eventually want to stop using .build) which should be gitignored and it'll be stored there