Add documentation for Images API v2 image sharing

Image sharing was added to the Images API v2 for the Grizzly release
but was not documented in the API Reference or API Quick Reference.
This commit adds the missing documentation to the Image Service API
v2 Reference.

Also corrects image update example in Appendix A.

Change-Id: I263918ee81c8d7442cb6ef7764231b396a68b1ff
Partial-Bug: #1227801