Fix `create_submodule` when submodule exists
Fix `create_submodule` when submodule exists

Uses a workaround already accepted upstream to fix `create_submodule`
when the submodule already exists. In particular naming the submodule
with the user provided name. By being able to use `create_submodule`,
this script runs substantially faster than when calling `submodule`.
Reason being calling `submodule` lists all submodules in the repo and
then selects the one we named. Whereas `create_submodule` simply
provides us the requested submodule. So using this workaround is
necessary for the performance improvement it provides.

ref: https://github.com/gitpython-developers/GitPython/pull/679

conda-forge/conda-forge-webservices,conda-forge/conda-forge-webservices