fix urls in 'description' fields in image schema

[Brian Rosmaita]

The image schema contains docs urls in some 'description' fields (for example, for the "common image properties"). These are problematic because it's not obvious that it makes sense for them to point to the "latest" docs.

Need to research whether the urls should point to 'latest', or to 'stable/whatever', or would it be better not to have the urls at all? (Maybe just something like "Please refer to your deployment specific documentation what properties and values are used")