Migrate managed identity example to azidentity

[chlowell]

github.com/Azure/go-autorest/autorest/adal is no longer supported, having been replaced by github.com/Azure/azure-sdk-for-go/sdk/azidentity

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.70%. Comparing base (b3a8513) to head (f98dd81).

Additional details and impacted files

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##             main     #199   +/-   ##
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  Coverage   74.70%   74.70%           
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  Files          32       32           
  Lines        6344     6344           
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  Hits         4739     4739           
  Misses       1323     1323           
  Partials      282      282           

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[shueybubbles]

the azuread package already supports managed identity auth via the connection string if you use azuread.DriverName as the driver name . Might it be better to have the example use that package now?

[chlowell]

Up to you--if there's a better pattern for managed identity that uses a supported library, highlighting it in this example seems like a good idea to me. I'm not familiar with the API here, this PR is just the smallest change required to remove adal from the example.