code: public ModifyColumnFamiliesRequest addFamily(String familyId, GCRule gcRule) {
      Preconditions.checkNotNull(gcRule);
      Modification.Builder modification = Modification.newBuilder().setId(familyId);
      modification.getCreateBuilder().setGcRule(gcRule.toProto());
      modFamilyRequest.addModifications(modification.build());
      return this;
    }
docs: Configures the name and GcRule of the new ColumnFamily to be created
  
  @param familyId
  @param gcRule
  @return