Expand form for generating bundle variations

Problem/Motivation

Within task #3588544 we added a form to generate bundle variations from combination of multiple products and their child variations which works well.

But there are some caveats
* creating same bundle with different quantities is not possible because we use only sku of child variations to create bundle variation sku - add option to include quantities and parent product id
* if shop has 2 products with 10 variants each, current way we will generate 20x combinations. Maybe not all combination are desired and required - so we need to load child variations upon selecting product, to be able to reduce desired combinations

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes