Update Git submodule via commits API

Description

In order to be able to automate some workflows, we are currently seeking a way how to update the commit SHA of a submodule via Gitlab's Commits API.

Proposal

Imagine you have updated a submodule with some changes, etc. and you now want to update all the projects which are using this submodule to this specific commit SHA. Besides updating "normal" files, the Gitlab Commits API should also be able to update the Commit SHA of submodules.