Use JDBC cursors for SQL client streaming

[vietj]

The implementation of the SQL client streaming with JDBC will load the entire results set in memory. Here is a short description on how to proceed for the implementation:

JDBCPreparedQuery has an optional cursorId and fetch values indicating whether the query should or not use a cursor to execute the query

We likely need a Map<String, JDBCPreparedQuery<?, ?>> that keeps the prepared queries holding the ResultSet

When a non null cursorId is provided

• the action should be created the first time and the action should create the ResultSet that holds a cursor. This ResultSet is cached on the action so it can be reused multiple times
  -the action should be looked up in the map and reused instead of being created otherwise

When an action is executed and provides its result it gives a boolean indicating whether the end has been reached:

  private <R> void handle(JDBCQueryAction<?, R> action, QueryResultHandler<R> handler, Promise<Boolean> promise) {
    Future<JDBCResponse<R>> fut = conn.schedule(action);
    fut.onComplete(ar -> {
      if (ar.succeeded()) {
        ar.result()
          .handle(handler);
        boolean suspended = false; // Set to true for result set still having results
        promise.complete(suspended);
      } else {
        promise.fail(ar.cause());
      }
    });
  }