Perturbation/Increments for cold starts

Description

Currently the model can only read in an increment file if initializing with a restart file. This functionality is also used to read in ensemble perturbations, and should also work for a external initial condition. The solution is to move the call to read_da_inc outside the if external_ic/restart logic.

There should be no changes to any regression tests.

Issue(s) addressed

fixes [NOAA-GFDL/GFDL_atmos_cubed_sphere/issues/339]

Testing

How were these changes tested?
I used a regression test sandbox to compare a non-pertrubed run (which passes the RT) with a new perturbed run, and the differences are what I expect. What compilers / HPCs was it tested with?
gaea - intel Are the changes covered by regression tests? No, for some reason there is no checking of the read_da_increment capability anymore. Have the ufs-weather-model regression test been run? On what platform?
Not the full suite

Will the code updates change regression test baseline? If yes, why? Please show the baseline directory below. -No
Please commit the regression test log files in your ufs-weather-model branch

Dependencies

If testing this branch requires non-default branches in other repositories, list them. Those branches should have matching names (ideally)

Do PRs in upstream repositories need to be merged first? If so add the "waiting for other repos" label and list the upstream PRs

waiting on [NOAA-GFDL/GFDL_atmos_cubed_sphere/pull/340]

NOAA-EMC / fv3atm