add stock - cannot add new variation of a product if an existing variations exists in cart

[nikhil96widhani]

Fixed by changing full logic but needs testing as api was written by @mohitdevda2797 .

To test:

1. add a variation and try to add same variation again(should not add because you cannot add same variation 2 times in bill items)
2. add a variation> click is new variation and then add same variation again (this time it should add because the other variation is going to be a new variation )

[nikhil96widhani]

TO FIX:

checkbox can be disabled for 2 items after adding to the bill thus making it a duplicate update!!!

[nikhil96widhani]

Fixed above but but now all toast are green Colour. @mohitdevda2797 write a Classification ML algorithm to identify if the message type an error or a success.