Document WorkerVersion.feature and arkindex update_system_workers

• docker.* settings removed
• The system checks W014 and W015 have changed
• New E012 system check introduced to prevent releasing without checking the update_system_workers images
• The first run after setting up Arkindex should include a call to update_system_workers
• The 1.6.3 upgrade notes should be created and document all of those changes, while recommending to run update_system_workers on every subsequent deployment