Add APIs to create and manipulate snapshots

This adds a new action on stacks to snapshots them, and specific actions
to show and delete them.

blueprint stack-snapshot
Co-Authored-By: ala.rezmerita@cloudwatt.com

Change-Id: I225b199f3a25a0b40653d654d7fab8cf9de3f242
Merge "Add APIs to create and manipulate snapshots"