[account_global_discount] Discounts are showed in invoice lines

[alvaro-domatix]

In version 15.0, when you applied global discounts to invoices, they were not shown in the invoice lines or invoice reports. Now, in version 16.0, they are shown. This may not be a problem for single-line invoices, but it is for invoices with multiple lines.

I would like to know if there is any reason for this change, and if there is not, propose to revert it to the previous behavior. I would appreciate feedback in order to address this issue properly.

In this comment, @rafaelbn shows what I'm trying to explain: #1338 (comment)

@ferran-S73 @pedrobaeza

Thank you

[ferran-S73]

I don't recall any specific reason for discount lines to be in the invoice tab. Maybe they should be created with a different display_type. Unfortunately I can't really tell you which type maybe someone with more accounting knowledge can help