Add support for anonymous Azure blob access

[agocke]

The current support for Azure blob storage can't deal with the situation where the blob store needs to be accessed anonymously. This PR adds the opendal http backend and an environment variable that can be used to enable Azure anonymous access. If the environment variable is set, sccache falls back to direct http access instead of the opendal authentication flow.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.46%. Comparing base (0efe890) to head (4914aea).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2610      +/-   ##
==========================================
+ Coverage   73.40%   73.46%   +0.06%     
==========================================
  Files          68       68              
  Lines       37219    37316      +97     
==========================================
+ Hits        27320    27416      +96     
- Misses       9899     9900       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[sylvestre]

some jobs are failing

[agocke]

Thanks, investigating.

[agocke]

I believe this is ready for re review/testing

[sylvestre]

The toml_format job is failing