WHAT
OHSS-10268 is completed so ROSA STS stage clusters can be created using the AWS account. 

The delorean script should be updated to default to use stage and also the oidc url in the script is slightly different, so will also need to be updated to support the stage environment

HOW
[1] should be updated to "staging"

[2] should be updated dynamically depending on whether the cluster is created in stage or production

[1] https://github.com/integr8ly/delorean/blob/master/scripts/sts/sts.sh#L42
[2] https://github.com/integr8ly/delorean/blob/master/scripts/sts/sts.sh#L102

TESTS
<List of related tests>

DONE

• Cluster is defaulted to stage
• Correct oidc url is used depending on cluster environement