Automatic schema detection

[pwoods25443]

Detect the schema automatically for messages from the source table or query.

For the table, this is easy, just use the Bigquery API and get the schema. For a query, some possible things to try

• Create a view with the query, get the schema of the view, then delete the view
• Run the query and put the output into a temporary table. Use this table as the input, and delete the table when you're done
• figure out how to get the schema out of io.gcp.bigquery.BigQuerySource. It is retrieved in the reader when the first row of data comes back, so if we can get it out of there and make it available to the later stages, that will be nice

[pwoods25443]

This is currently working if you specify a table as the source, but not if you specify a query or a file