create an alias when record in a zone another than the target

[epollia]

Description

DNS cannot work with cname whose target is another domain.
Example (This cname does not work.):
ads.localhost in google.com CNAME

But PowerDNS can create ALIAS
This PR changes the pdns provider to create aliases for such entries. This is required when k8s uses alb/nld on AWS etc.

Checklist

• Unit tests updated
• End user documentation updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: epollia (16b8192)

[tommy31]

Hey,
This issue is related to #3253. Same enhancement is required for gandi.
Maybe we should find a solution at the core level of external-dns and not in each provider as this seems comons to use ALIAS on a lot a providers.
Regards

[ngnix]

Hey guys, do you have any update?

[reyvonger]

any update?

[szuecs]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[tmaroschik]

@tommy31 and @szuecs This change is intentionally good, but it affects all non-apex records in pdns aswell and creates aliases for records that should be CNAME. So it introduces a bug.

See: #3970