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.