Use Parallel.ForEach(...) to forward records in child processor inside one topology

Description

At time, forwarding records in child processor inside topology is synchronous.

        public virtual void Forward<K1, V1>(K1 key, V1 value)
        {
            log.Debug($"{logPrefix}Forward<{typeof(K1).Name},{typeof(V1).Name}> message with key {key} and value {value} to each next processor");
            foreach (var n in Next)
                if (n is IProcessor<K1, V1>)
                    (n as IProcessor<K1, V1>).Process(key, value);
        }

Aims of this ticket is to propose a parallel execution like that :

        public virtual void Forward<K1, V1>(K1 key, V1 value)
        {
            log.Debug($"{logPrefix}Forward<{typeof(K1).Name},{typeof(V1).Name}> message with key {key} and value {value} to each next processor");
            Parallel.ForEach(Next, (n) => n.Process(key, value));
        }

Test to execute :

• No regression in stateless processor
• No regression in statefull processor

[vimal-sivasubramanian]

@LGouellec, We can address the above mentioned issue with the following code,

Parallel.ForEach(Next.OfType<IProcessor<K1, V1>>(), p => p.Process(key, value));

when we have to filter by name we can make use of linq to perform the same

var processors = Next.OfType<IProcessor<K1, V1>>() .Where(p => p.Name.Equals(name));

[joaovitorpina]

@LGouellec I oppened a pull request pertaining this issue, let me know what you think! #153