Turn on DC for ABP Premium users by default

Background / User story

Users who upgrade to Premium have to manually turn on DC at the moment. As a user that upgrades specifically for DC as it's the main perk, I would like to benefit from it right away.

What to change

• Design: –
• Research: –
• Spec: spec!417 (merged)
• Legal: –
• Development: Turn on DC by default for users who upgrade to Premium.

Hints for testers

Please check whether the premium list is automatically subscribed to after users upgrade to premium.

Hints for translators

N/A