Configuration system rewrite

[jchristgit]

Migrating over what we discussed in the all-hands meeting here for the back end team to discuss

The configuration system rewrite is a big project which we want to do due to
problems with the current approach to managing configuration.

The new configuration system should provide us with the following features:

• Distinction between editable and non-editable settings. Some values should
  be able to be configured during the event, some should be immutable. The
  configuration system should have a built-in notion of this. For settings that
  will not change over the course of the event and need to be present at event
  start (such as the mail server to use), it may be clean to resort to the
  direct Django settings, as Django already provides functionality to work with
  this.

  • An example package that we could maybe take inspiration of would be
    django-constance.

  • Either way, we should expand the amount of settings that are configurable by
    the user in the frontend instead of further locking it down.

  • This should also take into account the possibility of a future cloud
    offering, although we still need to discuss what this means in terms of
    config system architecture.

• Simple unit testing. Currently, we lack a clean context manager or similar
  ways of overriding config values for a single unit test, and instead have to
  resort to setting values manually. In case of test failure, this results in
  cascading failures, making it harder to find the source of the issues.

• Note that the app is built on the assumption that it only runs for a single
  event - for more than one event we would probably use a coordinator service.

After reviewing additional requirements that we want here, and clearing the
small remaining backlog for core, create an issue to plan out the new
configuration system.