As per the postgreSQL JDBC driver [implementation](https://github.com/pgjdbc/pgjdbc/blob/ab2a6d89081fc2c1fdb2a8600f413db33669022c/pgjdbc/src/main/java/org/postgresql/PGProperty.java#L99), the default record fetch size is 0(which means, it caches all record)

This fix enforces default record fetch size as 10 to enable streaming of data.

Author: Prince J Wesley <princejohnwesley@gmail.com>

Closes #14502 from princejwesley/spark-postgres.