docs: Updating the samples "what's new" for API 7.1

"What's new" page hadn't been updated since 6.0 (18 months ago).
Replacing the old "new" sample apps with the three new ones added
for 7.1.

Doc is staged to:

http://go/dods-stage/samples/new/

bug: 32212333
Change-Id: Ibb48bb531c0d519e50d940d443b461a215ed87d7