Refactor azure private dns auth

[sfc-gh-jelsesiy]

Add common config to be shared by both azure and azure-private-dns providers
Update tests & docs

Checklist

• Unit tests updated
• End user documentation updated

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[sfc-gh-jelsesiy]

I signed it

[sfc-gh-jelsesiy]

/assign @Raffo

[sfc-gh-jelsesiy]

@njuettner @Raffo Could you take a look please? Would be great to get this out soon.

[Raffo]

@sfc-gh-jelsesiy I've some time budgeted for this today.

[Raffo]

Apart a minor comment, changes look good to me. Did you test the various way to authenticate on a real azure cluster?

[sfc-gh-jelsesiy]

Apart a minor comment, changes look good to me. Did you test the various way to authenticate on a real azure cluster?

@Raffo Thanks! I made the suggested changes and yes I have this versioning running in various production deployments

[Raffo]

/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Raffo, sfc-gh-jelsesiy

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