[Backort to release/3.0] - Expose componentId that is unique per request inside the channel-manager

Certain javascript components require a unique ID per request when used in the Channel Manager but not outside of the Channel Manager (the id should be unique per component but stable per request). Currently the closest we can get is using the hst.namespace tag but that is not unique per request (e.g. re-ordering two components in a container).
Although this can be done in FreeMarker and JSP this is not ideal.