[AWS] Adjust TTL for alias records

[Sewci0]

When using CNAME record with a TTL != 0, external-dns will continuously keepUPSERTING the record due to a difference in TTL. As per https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/resource-record-sets-choosing-alias-non-alias.html TTL for alias records is always set to the default value of 300s and can not be modified.

Steps to reproduce:

1. Create a CRD

apiVersion: externaldns.k8s.io/v1alpha1
kind: DNSEndpoint
metadata:
  name: test-example
spec:
  endpoints:
  - dnsName: test.example.com
    recordTTL: 60
    recordType: CNAME
    targets:
    - <ELB_TARGET>

2. Wait for the record to be created
3. Restart external-dns to invalidate caches.
4. Desired change: UPSERT test.example.com

Checklist

• Unit tests updated

[johngmyers]

Thanks!
/lgtm
/assign @seanmalloy

[szuecs]

/ok-to-test

[johngmyers]

/lgtm

[szuecs]

/approve

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