[16.0][ADD]pos_sale_order_fixed_amount

[adasatorres]

This add‑on lets you create fixed‑amount down payments directly from the Point of Sale. The same functionality is already available in later versions through the built‑in pos_sale module.

[adasatorres]

Don't merge — I found an error with pos_sale_order_print compatibility. Correction needed."

[adasatorres]

@Christian-RB Fixed.

[github-actions[bot]]

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