feat: Add hint for POLARS_AUTO_USE_AZURE_STORAGE_ACCOUNT_KEY to error message

[nameexhaustion]

• Adds a hint to set the environment variable POLARS_AUTO_USE_AZURE_STORAGE_ACCOUNT_KEY in the error message if it is unset and a cloud operation to Azure fails.
  • ref feat: Make automatic use of Azure storage account keys opt-in #20652 (comment), this may save some future users from having to go through the same debugging
• CredentialProviderAzure is now auto-initialized if the above is set (and we are able to successfully retrieve the keys) regardless of whether azure.identity is not installed, as in this case we don't use the library.

[codecov]

Codecov Report

Attention: Patch coverage is 38.70968% with 19 lines in your changes missing coverage. Please review.

Project coverage is 79.30%. Comparing base (6a3fc59) to head (25d9056).
Report is 57 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-io/src/cloud/polars_object_store.rs	28.57%	10 Missing ⚠️
py-polars/polars/io/cloud/credential_provider.py	35.71%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20942      +/-   ##
==========================================
- Coverage   79.30%   79.30%   -0.01%     
==========================================
  Files        1578     1578              
  Lines      224135   224156      +21     
  Branches     2574     2576       +2     
==========================================
+ Hits       177751   177758       +7     
- Misses      45793    45807      +14     
  Partials      591      591              

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