Remove parameter_keys from Ridge and create utility that allows easy removal of gradients or values

[agoscinski]

See last comment metatensor/metatensor#96

We do not do the proxy. We will use the remove_gradients function, to remove gradients and then in equisolve we just apply the model on everything that exists in the TensorMap.

https://lab-cosmo.github.io/equistore/latest/reference/python/operations/manipulation/remove-gradients.html#remove-gradients