Change object_name to object_id in _pico_privilege
In order to support renames in the future use object_id instead of object_name
While at it, lets change order of fields as well to match "grant read on table X"
I ended up with this definition:
pub struct PrivilegeDef {
pub privilege: String,
pub object_type: String,
pub object_id: u32,
/// Id of the user or role to whom the privilege is granted.
///
/// In tarantool users and roles are stored in the same space, which means a
/// role and a user cannot have the same id or name.
pub grantee_id: UserId,
pub grantor_id: UserId,
pub schema_version: u64,
}