XIOS metadata and related code is found only in lfric_atm/gungho

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

For checkpoint/restart and diagnostics, lfric_atm relies on XIOS metadata to define and control various IO operations. Related code is in science/gungho.

As all the metadata and code is in lfric_atm/gungho, other applications are not able to use the same functionality.

The system needs to be refactored to deliver generic capability that can be shared by any app.

### Further details of the issue.

_No response_

Start by reading the XIOS metadata and related code under lfric_atm/gungho, then compare how other applications handle checkpoint/restart and diagnostics. Define the shared generic capability and verify that it can be used beyond lfric_atm/gungho.

Written by the indexing model from the issue text.