Add support for git-submodules ecosystem metrics collection

[amazimbe]

What are you trying to accomplish?

Update the git-submodules ecosystem to add support for gathering ecosystem metrics.

Anything you want to highlight for special attention from reviewers?

This is one in a series of PRs to gather ecosystem meta data and persist it in datadog.

These metrics don't include language information because language does not seem to be applicable to git-submodules.

How will you know you've accomplished your goal?

• I'll be able to see git-submodules ecosystem metrics in datadog

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.