feat: Make automatic use of Azure storage account keys opt-in

[nameexhaustion]

ref #20634

• Fixes a behavior where storage account keys retrieved from Azure CLI would in some cases override user-specified configurations
• Disables retrieving and using storage account keys from Azure CLI by default, this is now only done if POLARS_AUTO_USE_AZURE_STORAGE_ACCOUNT_KEY=1 is in the environment (note that azure.identity must also be installed as well, so that CredentialProviderAzure gets instantiated)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 79.02%. Comparing base (dd9a180) to head (46f6001).
Report is 51 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/polars/io/cloud/credential_provider.py	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20652      +/-   ##
==========================================
+ Coverage   79.00%   79.02%   +0.02%     
==========================================
  Files        1559     1559              
  Lines      221216   221151      -65     
  Branches     2529     2530       +1     
==========================================
- Hits       174761   174758       -3     
+ Misses      45876    45814      -62     
  Partials      579      579              

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[nameexhaustion]

Authentication will now prioritize Entra ID (via the Python-side DefaultAzureCredential if azure.identity is installed). Using the storage account key will only happen if we get a permission error (above).

[nameexhaustion]

PR has been updated to remove the fallback mechanism, I don't have any ideas for a good way to determine whether the Azure object store has sufficient permissions - according to #20634 (comment), attempting to fetch a random file path is not good enough as there can be file-level RBAC configurations on the bucket.

Instead, if POLARS_AUTO_USE_AZURE_STORAGE_ACCOUNT_KEY=1 is set, the Python-side Azure credential provider will prioritize using storage account keys if they can be found from the Azure CLI. Otherwise, credential resolution is left to DefaultAzureCredential.