Add the unbalanced ssh std dev to B

[guillaumevernieres]

This PR does 2 critical things:
1 - Ensemble processing: Properly re-centers ssh arround the deterministic background, adding back $\eta_u$ to each perturbations
2 - D: Saving the std. dev. of $\eta_u$ in the file used to initialize D

[AndrewEichmann-NOAA]

Looks reasonable

[emcbot]

Automated Global-Workflow GDASApp Testing Results:
Machine: hera

Start: Mon Sep 11 20:49:33 UTC 2023 on hfe07
---------------------------------------------------
Build:                                 *SUCCESS*
Build: Completed at Mon Sep 11 21:52:41 UTC 2023
---------------------------------------------------
Tests:                                 *SUCCESS*
Tests: Completed at Mon Sep 11 22:38:54 UTC 2023
Tests: 100% tests passed, 0 tests failed out of 52

[emcbot]

Automated Global-Workflow GDASApp Testing Results:
Machine: orion

Start: Mon Sep 11 15:47:48 CDT 2023 on Orion-login-1.HPC.MsState.Edu
---------------------------------------------------
Build:                                 *SUCCESS*
Build: Completed at Mon Sep 11 17:07:39 CDT 2023
---------------------------------------------------
Tests:                                 *SUCCESS*
Tests: Completed at Mon Sep 11 17:42:00 CDT 2023
Tests: 100% tests passed, 0 tests failed out of 52