code: public Either<String, List<String>> dataSources(Map<String, String> reqHeaders) {
          Either<String, Either<JSONArray, JSONObject>> resp = fireCommand("druid/coordinator/v1/metadata/datasources", null, reqHeaders);
          if (resp.isLeft()) {
              return new Left<>(resp.left().get());
          }
          Either<JSONArray, JSONObject> goodResp = resp.right().get();
          if (goodResp.isLeft()) {
              JSONArray dataSources = goodResp.left().get();
              List<String> dataSourceList = new ArrayList<>();
              for (int i = 0; i < dataSources.length(); i++) {
                  dataSourceList.add(dataSources.getString(i));
              }
              return new Right<>(dataSourceList);
          }
          return new Left<>(resp.left().get());
      }
docs: Retrieve all the datasources provisioned in Druid.
  @param reqHeaders
  @return