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This adds support for all AWS Route53 routing policies, namely:
* simple (default)
* weighted
* latency
* failover
* geolocation
* multi value answer

These routing policies allow to create multiple records with the same
name, but different "SetIdentifiers". Therefor, as a prerequisite for
implementing support for above routing policies, there is a new
"abstraction layer" added that handles this SetIdentifier by adding a
new attribute in the Endpoint struct and adding another level in the
plan table.