add postgres version to subsequent helm deploys

What does this MR do?

Fixes an issue with autodevops: if the postgres image version isn't passed to upgrades, helm will revert to the default postgres version. If it crosses incompatible version boundaries, this will break postgres horribly, as it won't be able to read the data files.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

I'm not sure if there are automated tests for autodevops stuff, but I'm happy to try to integrate this into testing somehow.