Add support for using a git repository as the source of a module

[devblackops]

Description

This PR adds a new capability to New-POSHOriginResourceFromModule to reference POSHOrigin configurations stored in a git repository.

Related Issue

19

Motivation and Context

Allow pre-baked POSHOrigin configurations that are stored in source control to be referenced when defining new resources.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

  Checklist:

• [X] My code follows the code style of this project.
• [X] My change requires a change to the documentation.
• [X] I have updated the documentation accordingly.
• [X] I have read the CONTRIBUTING document.
• [X] I have added tests to cover my changes.
• [X] All new and existing tests passed.