Expose the derived ejb max pool sizes as runtime attrbutes

The max size of ejb pools can either be explicitly configured, or configured to be calculated by the server. The explicit config is done via an attribute named "max-pool-size", which for compatibility reasons can't be renamed or repurposed. But we don't provide any attribute that exposes the actually used value, whether it's explicitly set or calculated.

The RFE is to provide such an attribute. It would be a runtime-only attribute only available on the server.