SubDyn does not include pretension force in its outputs

[ebranlard]

Bug description
SubDyn does not include pretension force as past of outputs.

This issue is related to the fact that gravity was removed from the output, see:
https://github.com/OpenFAST/openfast/blob/main/modules/subdyn/src/SubDyn_Output.f90#L254
Introduced in commit 0631a9b

To Reproduce
Run the following test:
https://github.com/OpenFAST/r-test/tree/dev/modules/subdyn/SD_Cable_5Joints

Expected behavior
The pretension load is not present in the output forces.

OpenFAST Version
Current dev (as of October 2021), and ever since the cable feature was merged into main (2.6+).
Introduced in 0631a9b

[ebranlard]

Should be fixed with commit above. r-test will be updated and merged in a future pull-request.