Improve external object storage docs
Add examples for setting up the various components in object storage.
Add a section for setting specific to backups (the backup bucket, the tmp bucket, and the config)
Clarify what the expected secrets are meant to look like.
For example, registry is yaml, which is the same as it's docker registry documentation, which may be clear enough, but our other documentation does not mention that the fog settings should also be yaml, so it isn't clear how you would know to configure the connection settings for most of the non-registry config.