Add support for D7 upgrade projects

[Decipher]

Is your feature request related to a problem? Please describe

As a module maintainer I want to be able to start a DrupalPod from a D7 project with a D9 install so that I can upgrade the D7 module and test it in the D9 site.

Describe the solution you'd like

If a D7 project is used to start the DrupalPod, don't download it via Composer. Setup D9 and then download the D7 codebase via Git and symlink it in place.

Describe alternatives you've considered

Additional context

[Decipher]

I tested two examples of this:

1. A D7 version of a module that had a D8 release; It cause Composer to fail to download Drupal correctly.
2. A D7 version of a module that didn't have any higher releases; It downloaded the everything correctly, but didn't symlink the module into the D9 codebase.

[lostcarpark]

For D7 modules with no D8 version, Drupalpod seems to behave pretty well. The only thing missing is a symlink from modules/contrib to the repos/module_name directory. Creating the symlink during the Drupalpod spin-up would be useful, but I think it's something most users could handle manually.

For D7 modules with a D8 version, I'm not sure what the desired behaviour should be. I'm guessing there might be times when you would want to load the unmodified D7 module, and in those situation it should not require the module with Composer, and Download the D7 version to the Repos directory.

Related to this issue would be consideration of loading D8 modules for migration to D9, which may fail with Composer dependency issues. Perhaps adding a checkbox for the new Drupal "lenient" endpoint could help resolve these conflicts.