New feature: Sentinel 1 backscatter data assimilation and water cloud model RTM

[mbechtold]

At KU Leuven (research group of Gabrielle De Lannoy) we developed plugins for a Sentinel-1 backscatter data assimilation with the water cloud model as RTM.
The cleaned up branch with two DA cases:

• VV backscatter for soil moisture updating, and
• VV&VH backscatter for soil moisture and LAI updating
  can be viewed here
  https://github.com/mbechtold/LISF/commits/Sentinel1_DA_for_PR
  A testcase is provided in the lis testcases/dataassim directory of that branch

A pull request could be opened based on https://github.com/mbechtold/LISF/commits/Sentinel1_DA_for_PR. There are no conflicts with the current NASA-LIS/LISF/master.

The PR includes bug fixes related to

• the use of multiple observation types which we needed for the joint VV and VH assimilation
• issue Wrong use of DA instance index k in write out of spread and incr. #1012 that we found when assimilating VV and VH in two different instances (the approach of using two separate instances we eventually replaced by using the multiple observation type option)
• and a bug fix we encountered in the map_utils that occurs due to longitude 0/180 for the latlong projection. We adopted the correct approach that was already present in llij_gauss

First papers making use of the Sentinel-1 data assimilation:
https://hess.copernicus.org/preprints/hess-2022-61/
https://hess.copernicus.org/articles/25/6283/2021/hess-25-6283-2021.html