code: public CreateTableRequest addFamily(String familyId, GCRule gcRule) {
      Preconditions.checkNotNull(familyId);
      tableRequest.putColumnFamilies(
          familyId, ColumnFamily.newBuilder().setGcRule(gcRule.toProto()).build());
      return this;
    }
docs: Adds a new columnFamily with {@link GCRule} to the configuration. Please note that calling this
  method with the same familyId will overwrite the previous family.
  
  @param familyId
  @param gcRule