implement Array/Vector for serialization

[BeroBurny]

It could be something like this: https://github.com/ChainSafe/ssz/blob/master/src/types/composite/array.ts

export class UnboundedArray extends CompositeType {
   constructor(opts: {type}) {
   }

   serialize() {
     //impl
    }

       deserialize() {
     //impl
    }

   toJson() {
     //impl
    }

      fromJson() {
     //impl
    }

}

and use it instead of ListType in networkMetrics.ts

Originally posted by @mpetrunic in #327 (comment)