Dynamic add column

[randyh0329]

BigQuery can dynamic add column, is it a good idea to add this handling in plugin?

Avoid check the table schema every time, may add this in error handling.

code Logic may like: bq table has 5 columns

1. generate 5 columns data -> fluentd -> bq (normal flow)
2. generate 7 column data -> fluentd -> bq (error, trigger add column and retry)

Any suggestion?