This commit adds the ability to configure unique tags on snapshots
that are separate from the tags defined on the AMI. Anything applied
to the AMI will also be applied to the snapshots, but `snapshot_tags`
will override and append tags to the tags already applied to the snapshots
It didn't indicate its unit of size (GB), the default value was not
indicated, the fact that it ignores the user-given size when it is
smaller than the source AMI's snapshot size, and the fact that the
value is required when `from_scratch` is `true` all needed to be added.
Arthur Burkart
Rickard von Essen
Chris Lundquist
Jeremy Asher
Sijis Aviles
owjjh
Chris Bednarski