feat: add private theme and plugin repo support

Description

This MR adds support for using private theme repositories and downloading private edx plugins using git.

Supporting information

https://tasks.opencraft.com/browse/SE-5934

Testing instructions

Steps to test the changes:

1. TBD

Dependencies

N/A

Screenshots

If applicable, add screenshots to help explain your feature.

Checklist

If any of the items below is not applicable, do not remove them, but put a check in it.

• All providers include the new feature/change
• All affected providers can provision new clusters
• Unit tests are added/updated
• Documentation is added/updated
• The TOOLS_CONTAINER_IMAGE_VERSION in ci_vars.yml is updated
• The grove-template repository is updated

Additional context

N/A