Simplify how we obtein an asset

⚠ Pipeline failing until https://gitlab.com/coopdevs/pymasmovil/-/merge_requests/74 is published in a new version.

Update how the Asset class and its method "get_by_phone" obtains an asset. The order-item phone is an unique key for its corresponding asset, so we can directly call a "get asset" endpoint filtering by phone. There's no need to restrict the search within a given account where the asset is placed, like we did so far.