Make HNS check and client instantiation more reliable

[pjbull]

Issues #470 and #476 report problems with credentials being used that cannot determine if HNS is enabled on the storage account.

This fix does two things:

• First, we only create a new credential if it is of the type in _shared that is implemented in both libraries (SharedKeyCredentialPolicy). Other kinds of credentials are properly isolated to a shared underlying library in the Azure SDK codebase.
• Second, if the call to get_account_information results in ResourceNotFound, which indicates the credential does not have permission to get this metadata, we fall back to trying to see if the root dir in the container exists and has hdi_folder=True which should only be the case when HNS is enabled.

Closes #470

[github-actions]

🚀 Deployed on https://deploy-preview-478--gallant-agnesi-5f7bb3.netlify.app

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.2%. Comparing base (8207b3d) to head (5a6f116).
Report is 1 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff           @@
##           master    #478   +/-   ##
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  Coverage    94.2%   94.2%           
======================================
  Files          23      23           
  Lines        1745    1753    +8     
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+ Hits         1645    1653    +8     
  Misses        100     100           

Files with missing lines	Coverage Δ
cloudpathlib/azure/azblobclient.py	96.9% <100.0%> (+0.1%)	⬆️
cloudpathlib/azure/azblobpath.py	93.6% <100.0%> (ø)

[jayqi]

@pjbull looks good except for how this is documented in the changelog. I don't need to review again once you address that.