Image registry url in Online docs is incorrect

[siamaksade]

The integrated image registry url in the OpenShift Online docs refers to the "preview" url and needs to get updated to the url after GA:
https://docs.openshift.com/online/dev_guide/managing_images.html#accessing-the-internal-registry

Currently

$ docker login -u <user_name> -e <email_address> \
    -p <token_value> https://registry.preview.openshift.com

Should be

$ docker login -u <user_name> -e <email_address> \
    -p <token_value> https://registry.starter-us-east-1.openshift.com

[ahardin-rh]

Addressed via #4455 and the link is also fixed on the web console after discussion with the Online team.