Different postgres user per application

[maartenweyns]

For security purposes, different applications should use different users in our Google Cloud postgres instance. The users should have the minimal required privileges within their database.

Before merging this PR, it should be verified that the users in the google cloud postgres instance have the correct permissions!

Tasks:

• Create new users in Google Cloud postgres instance
  • events
  • dienst2
  • choice
  • listmonk
  • mand
  • areafiftylan
  • areafiftylan-legacy
• Update credentials in the application's secret file
• Update (reduce) permissions of the new user in the postgres instance
• Merge and pray everything works? :)

[maartenweyns]

By default, Google Cloud creates new users with the cloudsqlsuperuser role, basically meaning root access. These roles should be changed by hand per user with a psql client.