Reduce lfric_coupled test resolution

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

#494

### Brief description

Reduce the resolution of lfric_coupled test to C48ORCA1 to enable more frequent and less resource intensive rose-stem tests to be used.

This is a part of the larger Issue #494 to improve Coupled Model Testing capability in lfric_apps.

### Further details of the issue.

This will involve creating remapping weights for the new resolution, and introducing optional configs to allow future development of alternative testing resolutions with ease.

In addition, determine a suitable amount of resources to allocate to the tests at the new lower resolution and investigate whether it can run on a single node to further reduce resource requirements.