Add endpoint to duplicate a discount

[boherm]

Questions	Answers
Description?	Add endpoint to duplicate a discount. (improvement of the api ADR: PrestaShop/ADR#43)
Type?	improvement
BC breaks?	no
Deprecations?	no
Fixed ticket?	Fixes PrestaShop/PrestaShop#40281
Sponsor company	PrestaShop SA
How to test?	See PrestaShop/PrestaShop#40281

[paulnoelcholot]

Hello @boherm,

I tested you PR and it's good for me! 🎉

Thanks!

Test 1 :

Test 2 :

Test 3 :

Test 4 :

Test 5:

The changes have been successfully implemented on the back office.

[boherm]

Thanks @paulnoelcholot!