The update of the created_by and updated_by model fields in many
serializers can be simplified by extracting the logic into a mixin.

We have introduced a system for custom field write permissions that
allows administrators to control which users can write specific fields
in steering.

This system is based on specific model permissions in the form of:
	{app_label}.edit__{model_name}__{field_name}

This mixin makes it easy to check said permissions simply by including
it as part of the serializer.

API consumers must not be tempted to parse ids, so we encode them as
UUIDs to prevent that.

This new endpoint allows clients to easily purge steering’s application
state. It is primarily designed for use in integration tests as outlined
in aura#387.

The endpoint is available in debug mode so that developers can inspect
the schema. However, any request to it is denied unless the
OPERATING_MODE environment variable is set to "tests". This is a
precaution for administrators that use the debug mode to analyze
application issues in production.

feat: exclude internal_not, owner_ids and created & updated fields from show serializer for calendar

This reverts commit 072a351f.

This reverts commit d1681848.

This reverts commit 8d32fab1.

This reverts commit 906b8420.