state/apiserver: move api/params to apiserver/params

This PR moves `api/params` to `apiserver/params`. The justification is the `params` package defines the form of the api messages that the server will accept, not the form that the client will provide.

This move makes it clear that the parameters belong to the `apiserver`, not a Go implementation of the api client.
Super minor point, but I think for correct ordering the import would come after apiuniter.