Support for Postgresql 13

This issue for adding support to Jira for Postgresql, which was released 9/24/2020.

It would be much appreciated if support could be added to other server/data center products (e.g. Confluence) at around the same time. As a customer, being able to run each Atlassian product on the same database version reduces complexity, maintenance cost and ultimately the cost of ownership for Atlassian tools.

Having support available for more recent versions of postgresql gives us more flexibility in scheduling upgrades and gets us using newer versions more quickly – instead of waiting an indeterminate amount of time for Atlassian to add support for it, and only then being able to upgrade.