Provider PowerDNS implementation

[simcod]

What this PR does / why we need it:
Adds PowerDNS as additional provider.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release note:

Adds PowerDNS as additional provider

[CLAassistant]

All committers have signed the CLA.

[gardener-robot]

@simcod Thank you for your contribution.

[gardener-robot-ci-1]

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[MartinWeindel]

@simcod
Thanks for your contribution!

As I'm not very familiar with PowerDNS, can you explain, why it is not sufficient to use the the provider type rfc2136 for PowerDNS. According to the documentation it should support it.
Have you tried it?

[robertvolkmann]

Hi @MartinWeindel, we've opted to use the REST interface of PowerDNS to maintain consistency with the code base of our PowerDNS extension.

[MartinWeindel]

Thanks for your contribution. Implementation looks good to me.

Please add documentation about credentials secrets and examples.
Similar to:

• https://github.com/gardener/external-dns-management/blob/master/README.md?plain=1#L15
• https://github.com/gardener/external-dns-management/tree/master/docs/rfc2136
• https://github.com/gardener/external-dns-management/blob/master/examples/20-secret-rfc2136-credentials.yaml
• https://github.com/gardener/external-dns-management/blob/master/examples/30-provider-rfc2136.yaml

[simcod]

@MartinWeindel Thank you for your feedback.

I added documentation about credentials and examples.

[MartinWeindel]

/lgtm

Thanks for your contribution!