Petals BC SQL

There is a thread pool inside the SQL BC used to decorrelate execution of SQL queries and send of the JBI answer. When it was introduced, the idea was that we could send the JBI exchange even before the response was built because it was in the form of a stream that was put inside a StreamSource. But since PETALSESBCONT-327, sources are transformed to a re-readable source, so it must be read when it is set on the exchange which remove any reason for decorrelating sending and building the answer. Furthermore, this introduce complexity and redundancy with respect to the CDK thread pool that is already here to handle this kind of situation.