Submodule update options structure
Initialize with GIT_SUBMODULE_UPDATE_OPTIONS_INIT. Alternatively, you can
use git_submodule_update_options_init.
These options are passed to the checkout step. To disable checkout, set the checkout_strategy to GIT_CHECKOUT_NONE or GIT_CHECKOUT_DRY_RUN.
Options which control the fetch, including callbacks.
The callbacks to use for reporting fetch progress, and for acquiring credentials in the event they are needed.
Allow fetching from the submodule's default remote if the target commit isn't found. Enabled by default.