Nudging and Surface coupling issues for recent nudging simulations

There are a number of issues that come up when running a CIME based case w/ nudging turned on. This issue lists them so we can track progress on addressing them.

Nudging:
- [x] Typical output only provides `horiz_winds` as an option instead of `u` and `v` which is what is needed in nudging.
- [ ] Nudging source data may include masked values, which we do not want to include when interpolating data onto the simulation state. Could lead to strange nudging values.
- [x] Re: basic usage of nudging - nudging by itself not recognized for requesting tendencies as output, must use `compute_tendencies=all`
- [x] Re: basic usage of nudging - Cannot use `atmchange` to specify nudging params.
- [x] Nudging currently assumes all data is in only one file - expect to use multiple files for production runs.
- [x] Nudging expects P_levs (3D) but it should allow it to be a static field (1D)
- [ ] Update coarsened output to write out 1D static`P_levs`

Surface Export Replacement:
- [x] Not a big issue, but the names of surface export variables do not match the output names for a typical run, requiring a processing step on source data to change variable names.