code: public <T> MutateInBuilder arrayInsert(String path, T value) {
          asyncBuilder.arrayInsert(path, value);
          return this;
      }
docs: Insert into an existing array at a specific position
  (denoted in the path, eg. "sub.array[2]").
  
  @param path the path (including array position) where to insert the value.
  @param value the value to insert in the array.