Implement interfaces for Cost.

[thibaud-perrin]

[GuillaumeSachet]

Updated Proto in Services-api. (I did not make a branch on services-api-py)
Updated all cost strategy in digitalkin
Updated cost repository and cost servicer in local services provider.

I did not tests any of it, so there could be some fixes to do.

TODO
test local services provider with local proto and local digitalkin
update surrealdb table
now, we only input in surreal almost as received. We may want to multiply unit*cost. (maybe need to rename cost). Do we multiply before grpc ? Do we only store the result or also unit and cost ?