Introduces two new config options, 'db-max-pool-size' and 'db-max-overflow', allowing charms to configure oslo.db connection pool behaviour when rendering database connection settings. Closes-Bug: #2132315 Change-Id: I5c4088b631c5a5b6ed99b621b0ee245576307e0f Signed-off-by: Raven Kaur <raven.kaur@canonical.com>