add git credentials as input parameter

[danielhaap83]

Checklist

• I have read the Contributor Guide
• I have read and agree to the Code of Conduct
• I have added a description of my changes and why I'd like them included in the section below

Description of Changes

Added new argument credentials to the action which initializes the internal git client. The internal git client will be forced to use these provided credentials. In this way someone could add required credential for internal or private git repositories used in cargo crates.

Related Issues

#53

[Jake-Shadle]

Thanks!