Fully consume insert response.

R2dbcEntityTemplate.insert(…) now fully consumes the response from the INSERT call before continuing. Previously, we consumed only the first signal and continued then. A driver could emit a row and then an error signal and so the error signal would go unnoticed.

Closes #552.

src/main/java/org/springframework/data/r2dbc/core/R2dbcEntityTemplate.java

@@ -568,8 +568,8 @@ private <T> Mono<T> doInsert(T entity, SqlIdentifier tableName, OutboundRow outb
 		return this.databaseClient.sql(operation) //
 				.filter(statement -> statement.returnGeneratedValues())
 				.map(this.dataAccessStrategy.getConverter().populateIdIfNecessary(entity)) //
-				.first() //
-				.defaultIfEmpty(entity) //
+				.all() //
+				.last(entity)
 				.flatMap(saved -> maybeCallAfterSave(saved, outboundRow, tableName));
 	}