[IMP] point_of_sale: Add unit on order line receipt

[rousseldenis]

This is the continuation of #98332

As auditors want to have same display between POS and receipt, this fixes that.

POS (current display):

Receipt (this change):

@pimodoo Thanks. The other one merged too fast 😅

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[robodoo]

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[C3POdoo]

Dear @rousseldenis,

Thank you for your contribution but the version 14.0 is no longer supported.
We only support the last 3 stable versions so no longer accepts patches into this branch.

We apology if we could not look at your request in time.
If the contribution still makes sense for the upper version, please let us know and do not hesitate to recreate one for the recent versions. We will try to check it as soon as possible.

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