Add submodules support on GitHub through `graphql` api

:clipboard: **Description**

Currently, more and more projects use git submodules to split the project architecture, leaving an almost empty main repository (almost only references to submodules)

However, when counting data such as repo size/code size/comments, shields does not take the data of submodules into consideration.

Currently, GitHub GraphQL Api can already query submodules under a warehouse.
As long as the recursive search (specifying the front depth) is required, a submodule tree of the warehouse can be constructed.
The shields (repo size, etc.) mentioned above can be more accurate. (Of course, we may have to verify that the repositories belong to the same owner)

Take my own repo for example:


Start by locating the existing repository-size, code-size, and comment data entry points and their GitHub GraphQL queries; the issue provides no file or test names. Clarify recursive depth and same-owner handling, then define tests showing that eligible submodule data is included in the affected shields.

Written by the indexing model from the issue text.