tf-stage1: standardize on TTL 3600 for DNS records

Almost all of our DNS records have a TTL of 86400 (24 hours) with a few
using a TTL of 600 (some MX and TXT records). The former is too long to
be flexible when a need for fast change(s) arises, and the latter don't
benefit from the low TTL. Standardize on a TTL of 3600 (1 hour) for all
our records.