Format of the hash key. The default is "{Host}".
            The format can include environment variables, attributes from the logged message, or can
            be a constant value.
            
            Environment variables are specified like so: %ComputerName%
            Attributes are specified like so: {Host}
            For example: {Host}-{EventType}-{ProcessId} or %ComputerName%-{EventType}-{ProcessId}
            
            Config key: HashKeyFormat
            
 Declaration Syntax
 Declaration Syntax| C# | 
public string HashKeyFormat { get; set; }