Add an indicator to the Statement object that it should be closed after use

[steveannett]

Currently when using a Statement object there is no indication for the underlying implementation whether the statement should be closed or left open.

It would be good if Statement.java could have a boolean value that could be set when building that could indicate to the implementation that the user wishes to close the statement, e.g. Statement releaseAfterwards();

[Mark Paluch]

We don't have a notion of 'open' in R2DBC, so we cannot introduce a notion of closing statements.

I understand the desire to close prepared statements at some point. Not all statements qualify for closing, only those that require server preparation.

In the drivers where this applies, drivers decided to provide a configurable strategy (FIFO, round robin, close after use) to release statements.