code: public Optional<PartnerUser> create(long partnerId, long accountId, PartnerUser user)
      {
          return Optional.of(HTTP.POST(String.format("/v2/partners/%d/accounts/%d/users", partnerId, accountId), user, PARTNER_USERS).get().iterator().next());
      }
docs: Creates the given user.
  @param partnerId The id of the partner the user belongs to
  @param accountId The id of the account for the user
  @param user The user to create
  @return The user that was created