[IMP] stock_account: add button to create manual stock valuation layers

Add a way to create a munual stock valuation layer, create
a stock valuation layers implies :
- Change the stardard price with the new valuation by product unit in case of AVCO.
- Create a manual stock valuation layer with the added value.
- Update the remaining value of current valuation layer.
- If the Inventory Valuation of the product category is automated, create
related account move.

task-2123752