[TASK] Setup and migrate to Heroku database

[bagelface]

Description

Setup and migrate the Notion integration service data storage solution to the Heroku-hosted Postgres instance.

Acceptance criteria

• A Postgres instance is setup on Heroku.
• The service deployment connects to this database.
• The current data is migrated using the migration scripts included in the dev branch.
• Any relevant clean up is completed

Additional context

Due to the current Notion data store being out of date, a migration to the database will result in spamming Discord messages. Because of that, we've decided that the best approach will be to migrate to staging with the data.json -> postgres approach. And to production with a postgres -> postgres migration. This will require the migration scripts to be updated.