fix product export of configurable_variations for configurable products with multiple super attributes

[rhoerr]

Description (*)

Default export functionality outputs invalid data for configurable products having more than one super attribute.

Column configurable_variations should contain all child SKUs, with the unique super attribute values of each one.
Instead, it outputs only the first SKU matched for each super attribute value.

Invalid, with attributes color and size: Note that most SKUs do not include both size and color. Only one row is output for each size and each color. (I put each SKU on a new line for clarity.)

sku=ABC-BM,color=Black,size=Medium|
sku=ABC-RM,color=Red|
sku=ABC-NM,color=Navy|
sku=ABC-BS,size=Small|
sku=ABC-BL,size=Large|
sku=ABC-BXL,size=XLarge|
sku=ABC-BXXL,size=XXLarge

Corrected: All child SKUs are output, with all super attribute values for each.

sku=ABC-RS,color=Red,size=Small|
sku=ABC-RM,color=Red,size=Medium|
sku=ABC-RL,color=Red,size=Large|
sku=ABC-RXL,color=Red,size=XLarge|
sku=ABC-RXXL,color=Red,size=XXLarge|
sku=ABC-NS,color=Navy,size=Small|
sku=ABC-NM,color=Navy,size=Medium|
sku=ABC-NL,color=Navy,size=Large|
sku=ABC-NXL,color=Navy,size=XLarge|
sku=ABC-NXXL,color=Navy,size=XXLarge|
sku=ABC-BS,color=Black,size=Small|
sku=ABC-BM,color=Black,size=Medium|
sku=ABC-BL,color=Black,size=Large|
sku=ABC-BXL,color=Black,size=XLarge|
sku=ABC-BXXL,color=Black,size=XXLarge

The issue was the core code iterating over super attributes and options (one match for each separate value), not over the combinations of super attributes and options (one match for each combination of values). I changed the loop to iterate over assigned child products and then output each super attribute in order, for each one.

Related Pull Requests

N/A

Fixed Issues (if relevant)

1. No related issues that I've seen

Manual testing scenarios (*)

1. Have a product with two or more configurable attributes.
2. Export that product.
3. Examine the export configurable_variations to confirm whether all child products and options are represented.

Questions or comments

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)