[feature] Read Start URL and Region via Environment Variables

[theurichde]

Describe the solution you'd like
Read the start URL and region from environment variables

Additional context
I would like to read the needed variables / flags via environment variables, like

AWS_DEFAULT_SSO_START_URL="https://my-login.awsapps.com/start#/"
AWS_DEFAULT_SSO_REGION="eu-central-1"

The chain should be

1.) Saved Config
2.) Environment Variables
3.) CLI Flags

where the predecessor always gets overridden

[bfanyuk]

And also aws profile to update :)

[theurichde]

I moved this issue to discussion as it was stale for 5 months.

When there is a dedicated need for this feature, I will implement it. But for now there is simply no need.