Add dataatm setup for coupled experiments

Description

Currently, there is no dataatm configuration for coupled experiments that works out of the box. Users attempting to run coupled experiments with a data atmosphere component must manually configure the setup, which is error-prone and creates an unnecessary work for users.

Problem

• No turnkey dataatm setup exists for coupled experiments.
• Users must manually configure the necessary files and settings, with no standardized or documented reference configuration.
• This gap is inconsistent with the expectation that standard experiment types are launchable via gcm_setup.

Proposed Solution

• Create a default, fully functional dataatm setup for coupled experiments.
• Integrate the new setup into the gcm_setup script so that users can select and generate it as part of the normal experiment configuration workflow.
• Ensure the setup runs out of the box with zero manual intervention.

Acceptance Criteria

• A dataatm coupled experiment can be selected and configured through gcm_setup.
• The generated experiment runs to completion without manual edits or additional configuration.
• Documentation/comments are updated to reflect the new option.