Add support for creating mapping files with `mbtempest`

[xylar]

This merge adds support for creating mapping files with mbtempest in addition to ESMF_RegridWeightGen. I have added moab with tempest-remap as a conda dependency.

Because mbtempest creates mapping files in 2 steps (first creating intersections and then creating the mapping file), I have modified the args attribute of Step to be a list of lists, allowing multiple commands. Each command is required to take the same parallel resources, which is fine for mbtempest.

I have added a new config file mapping.cfg with a [mapping] section and a map_tool config option (either esmf or moab). I have made moab the default.

Finally, I have updated the isomip_plus tests include the new mapping config.

Checklist

• [x] User's Guide has been updated
• [x] Developer's Guide has been updated
• [x] Documentation has been built locally and changes look as expected
• [x] Testing comment in the PR documents testing used to verify the changes

[xylar]

Testing

I successfully ran the ISOMIP+ Ocean0 planar, z-star test case at 4km resolution on Chrysalis. I ran with the default expansion factor of 2.0 as well as 1.0 and 4.0, verifying visually in ParaView that the resulting topography was smoother in proportion to the factor, as expected.