docs: Add 'description' field to domains

When the 'description' field got added for domains and records,
only the documentation for records was updated.

Also, fix minor domain schema error - the description for the
"created_at" and "updated_at" fields in domain.json is incorrect
in the v1 code base.

Change-Id: Id50ed109be81723da8e46e23f792173f435e0e3e
Fixes: bug#1213273
Merge "docs: Add 'description' field to domains"