Add options for building libraries for CM3

[blimlim]

Closes #324

This PR adds a driver variant to the access-cice spack package. This allows a custom relative path to be set for the CICE_DRIVER option in the CICE CMake build.

It also adds a MOM6-CICE6-UM13 build configuration to the access3 package, which adds gcom as a dependency when active, as suggested here. If we decide to it this way, this build configuration will also need to be added to the known configurations in the cmake build

[anton-seaice]

Is there a corresponding CMake change - the bigger part of this work is linking the UM into the access3 cmake right ?

[blimlim]

the bigger part of this work is linking the UM into the access3 cmake right ?

Definitely! At the moment I don't think the UM is ready to add, and so I'm hoping to start off just by cleaning up our current build process for CM3 in a way that shouldn't interfere with adding the UM in the future!

I think the corresponding CMake change for this will be to add a placeholder MOM6-CICE6-UM13 known configuration.

[anton-seaice]

Looks good - thanks @blimlim

Please squash merge and give a clear commit description