Hello Ajay,
We had said all commercial plugins would be open-sourced. With Postgres support, there is an attempt do something a little different by adding support for it within GoCD directly. The database access and migration part of GoCD is also being changed to make it be possible to use other database systems such as MySQL.
The pull request is here:
https://github.com/gocd/gocd/pull/7646
It is a work in progress and will likely be released in the next release or two. Please note that anyone who upgrades after it is released will need to run a data migration, even if they want to continue using H2. There will be documentation and tooling to help with it.
Cheers,
Aravind
PS: You should also see the rest of the plugins open-sourced starting this month. The first one will likely be the AWS elastic agent plugin.