Heroku Postgres upgrade (req. Oct 2025)

[grega]

The staging and production applications are using deprecated Postgres version 14 that will reach end-of-life on 2025-Nov-28.

Upgrades to at least version 15, but ideally 17, should be completed by 2025-Oct-28.

Documentation for the upgrade process can be found here: https://digital-docs.rpf-internal.org/docs/technology/infrastructure/heroku/heroku-postgres-upgrades

[chicgeek]

Slack channel for collaborating on upgrade topics: #digital-2025-heroku-upgrade