[New Azure Integration Pkgs] Port configuration provider to use the new Azure.Security.KeyVault.Secrets

[pakrym]

Updates implementation and most of the tests.

We need to decide on the new package name.

cc @anurse

[analogrelay]

@BrennanConroy can take a look for now. We'll get a meeting together to talk about the full plan for getting these in and shipping them somewhere.

[pakrym]

There is a bug with how ApiGEN generates namespaces, disabled ref assembly for now.

[BrennanConroy]

There is a stack overflow somewhere when running tests

[analogrelay]

Ok, we're good to re-visit this :). I'll take a scan now.

@pakrym can you retarget to release/3.1 and change the package name to Microsoft.Extensions.Configuration.Azure.KeyVault.Secrets as per the discussed plan? Let me know if you need resources from our end (I can put someone on this if your bandwidth has changed ;)).

We'll also need to get the versioning working. This should be versioned 3.1.0-preview1 even though it's in a patch branch.

Once all that's in place, I'll throw servicing-consider on this and we should be able to get it through Tactics since the plan has been Director-approved.

[analogrelay]

I'm not an expert on the functional changes though.

I have faith in your ability to read/review new code 😜.

[BrennanConroy]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jamshedd]

Approved for March.

[analogrelay]

We don't need this anymore! See aspnet/Announcements#408 .

Thanks again @pakrym