Configurable defaults for sso_start_url and sso_region in `aws configure sso`

Currently, `aws configure sso` is able to scan over the config file and pick up existing values of `sso_start_url` and `sso_region`, but the default (hitting enter) sets it to none. This is almost never useful when setting up a profile for AWS SSO. I would like the ability to set a default value for this, perhaps through environment variables, so that when I'm configuring a profile for AWS SSO, and I'm using my most-used AWS SSO provider (and I imagine that most folks only have one anyway), I can just hit enter on those first two and get to the meat of the profile config, the account and role name.