OCI Provider private zone and workload identity support

[anders-swanson]

Description

• Added support for OCI Private DNS zones via a new flag. Users of the Oracle DNS provider may now choose between Global, Private or Global+Private DNS zones when using external-dns.
• Updated the Oracle provider authentication methods to include Workload Identity.

Fixes #2326

Checklist

• Unit tests updated
• End user documentation updated

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[mloiseleur]

Thanks for this PR.
I have one question:

• Would it make sense to throw an error when both UseWorkloadIdentity & UseInstancePrincipal are configured ?

and also a suggestion:

• Would you please test this provider with a non-empty scope ?

[anders-swanson]

Thanks for the suggestions, I've incorporated both into the PR.

[mloiseleur]

/ok-to-test

[mloiseleur]

/lgtm

[anders-swanson]

@johngmyers looking for review/approvals when you have time

[szuecs]

@anders-swanson please start to migrate to webhook provider. I will approve anyways.

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: szuecs

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