Feature request: add inventory service

[GitGregOT]

Adding a HA service to inventory products using the "POST /stock/products/{productId}/inventory" on the Grocy API would be very useful for automatically determining the quantity of certain products based on sensors. This inventory action differs from buying/consuming because you can input the exact quantity of a product and let Grocy determine if it has to be added or subtracted on the database.
One very cool use case for this is to integrate pressure/weight sensors (scales) on HA with Grocy to get automatic inventory of a certain product, like a DIY, more integrated, and open source version of this: https://www.amazon.com/Dash-Smart-Shelf/dp/B07RRYWPPX .