add support for parameterized-queries in bqfrag

[ingarabr]

https://cloud.google.com/bigquery/docs/parameterized-queries

 String query =
  "SELECT word, word_count\n"
    + "FROM `bigquery-public-data.samples.shakespeare`\n"
    + "WHERE corpus = @corpus\n"
    + "AND word_count >= @min_word_count\n"
    + "ORDER BY word_count DESC";

QueryJobConfiguration queryConfig =
  QueryJobConfiguration.newBuilder(query)
     .addNamedParameter("corpus", QueryParameterValue.string(corpus))
     .addNamedParameter("min_word_count", QueryParameterValue.int64(minWordCount))
     .build();