WIP: Implement global configuration for object storage

• Convert all charts to use global.minio.enabled
• Move configuration of buckets and related secrets to global.objectStorage.x
• Convert unicorn, sidekiq and task-runner charts to make use of the new global settings and connections block secrets (Closes #532 (closed))
• Convert registry to be able to make use of the storage block as an external secret. (Closes #548 (closed))

Relates to #502 (closed)

I realized while creating this MR, that there are still lingering .Values.minio items present in the various charts. This will need cleaned up.

Documentation needs to be updated for these changes.