Bi-Directional Documents On Product/Bom

[Zephyria77]

Hello:

First of all thanks to all OCA by this hardwork.

I would like to propose a change in:
https://github.com/OCA/knowledge/tree/18.0/document_url

Actually document attached to product can visible at Sale and Bom.
In my opinion it could be useful if the option "visible at" was also available in Bom. Often the product has various bom with different feature but product remain the same (without variants)
This way the bom can have a correct documents and the product a complete view of his history or additive feature.

Thanks to all