roles feature flag in data_model causes serialization disparity

[mversic]

roles feature flag affects the layout of enums/structures in data_model because it conditionally includes/excludes variants/fields. Due to this, a difference can arise in serialized format on client as compared to the server which basically makes them unable to exchange some messages. Example:

pub enum WorldEvent {
    Peer(peer::PeerEvent),
    Domain(domain::DomainEvent),
    #[cfg(feature = "roles")]
    Role(role::RoleEvent),
    Trigger(trigger::TriggerEvent),
}

This can be fixed in following ways:

1. remove roles feature flag from all crates
   always include roles
2. remove roles feature flag from data_model crate only
   don't include roles in your data structures but always include them in the serialized form. Queries can work without problems with server just empty lists objects for roles. Instructions on roles must fail with an error. I'm not sure this is possible without implying the 1st point to always include roles. This possibility requires more consideration
3. Define initialization handshake
   Client will ask for the data layout information in the first message and adapt it's subsequent messages according to it. This effectively makes roles a compile flag on the server(as is currently) but a runtime flag on the client which adds strain on the sdk development
4. Include information about roles support in the schema
   I mention this possibility just out of completeness. I maintain that the 3rd point should take precedence compared to this one.

Relates to #1969
Could relate to #2112