Reason could be more specific for some situations

[JoeBatt1989]

Is your feature request related to a problem? Please describe.
Currently the FailureReason could be improved. i.e this is set as "None" when mandatory artefacts are missing. This is held in namespace Monai.Deploy.Messaging.Events

    public enum FailureReason
    {
        None,
        Unknown,
        RunnerNotSupported,
        InvalidMessage,
        PluginError,
        ExternalServiceError,
        TimedOut
    }

Describe the solution you'd like
Addition of further enums. Examples below

• "MandatoryInputArtifactsMissing"
• "MandatoryOutputArtfactsMissing"