Add generic SQL 2011 Spec-compliant R2dbcDialect

[mp911de]

We should consider adding a generic, SQL 2011-compliant R2dbcDialect as a general fallback for unknown drivers to allow DatabaseClient usage instead of failing with NoDialectException.

With #127, external libraries can contribute their own R2dbcDialect to handle dialect specifics. Providing a fallback for users that just want to use the execute() API enables these to do so instead of preventing usage.