Upgrade postgresql version to 18

[vuorioma]

#3451

Checklist for author

Remove items that aren't applicable, check items that are done.

Reviewability

• Link to issue
• Note if PR is on top of other PR
• Note if related change in rems-deploy repo
• Consider adding screenshots for ease of review

Backwards compatibility

• API is backwards compatible or completely new
• Events are backwards compatible or have migrations
• Config is backwards compatible
• Feature appears correctly in PDF print

Documentation

• Update changelog if necessary
• API is documented and shows up in Swagger UI
• Components are added to guide page
• Update docs/ (if applicable)
• Update manual/ (if applicable)
• ADR for major architectural decisions or experiments
• New config options in config-defaults.edn

Testing

• Complex logic is unit tested
• Valuable features are integration / browser / acceptance tested automatically

Follow-up

• New tasks are created for pending or remaining tasks

[pikariop]

Checklist should be updated but other than that it looks ready to me