object_store: When using an AWS profile, obtain the default AWS region from the active profile

[mr-brobot]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

When using a named profile via the AWS_PROFILE environment variable, the user must also supply an AWS_REGION environment variable even when the profile designates the desired region (in ~/.aws/config).

Describe the solution you'd like

I think object_store should default to the region designated on the active profile, when the aws_profile feature is active, to alleviate the need for a redundant environment variable.

Describe alternatives you've considered

We could just force users to supply AWS_REGION always, but that seems like unnecessary friction.

Additional context

This will improve the UX for CLI utilities that rely on object_store, like DataFusion CLI: apache/datafusion#6157

[tustvold]

label_issue.py automatically added labels {'object-store'} from #4161