Expose packs in catalog pricelist

CHANGELOG:

### ADDED
- [#867](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/867) Expose packs in catalog pricelist

Related card: https://trello.com/c/IJ1JJgqD/1376-identificar-en-lapi-de-cataleg-que-el-producte-pertany-a-un-pack

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