Create a role for managing one or more Route 53 DNS entries

[gregharvey]

Currently DNS entries are handled inline in roles like our EC2 instance role. This should be pulled out to a separate role that supports creating multiple DNS entries at once, and the roles that currently manage Route 53 should be refactored to make use of the new role.

[gregharvey]

Consider supporting TXT records too, like that we can handle DMARC and SPF as well (see #2424)