Fix bug where dependency variables reference and defaults were not being rendered

[yorinasub17]

Description

Fixes a bug that was introduced in https://github.com/gruntwork-io/boilerplate/pull/113 where the default and reference fields were no longer being rendered on direct variables definitions set on dependencies.

TODOs

Read the Gruntwork contribution guidelines.

• [x] Update the docs.
• [x] Run the relevant tests successfully, including pre-commit checks.
• [x] Ensure any 3rd party code adheres with our license policy or delete this line if its not applicable.
• [x] Include release notes. If this PR is backward incompatible, include a migration guide.
  • NOTE: The release notes below does not mention that we no longer support bare variable definitions on dependencies config, primarily because this is already captured in the v0.5.0 release notes.

Release Notes (draft)

Fixed bug where the default and reference fields were no longer being rendered on direct variables definitions set on dependencies.

[yorinasub17]

Thanks for review! Merging now.