fix(object_storage): make credentials optional for ABS/OSS/OBS/COS

[gaius-qi]

Description

This pull request refactors the credential handling logic for various object storage backends in object_storage.rs. The main change is to require only the endpoint field as mandatory for Azure Blob Storage (ABS), Alibaba Cloud OSS, Huawei OBS, and Tencent COS backends, while making access key ID and secret optional. Credentials are now set conditionally if provided, and test cases are updated to reflect the new requirements.

Credential Handling Refactor:

• Changed the initialization of ABS, OSS, OBS, and COS operators to require only the endpoint field as mandatory; access key ID and secret are now optional and set only if provided. This simplifies configuration and improves compatibility with different authentication methods. [1] [2] [3] [4] [5] [6] [7] [8]

• Updated builder logic for each backend to set credentials (access_key_id, access_key_secret, etc.) only if they are present, instead of requiring them up front. [1] [2] [3] [4]

Test Updates:

• Modified test cases to expect errors only when endpoint is missing, rather than when access keys are missing, aligning with the new credential requirements. [1] [2] [3] [4] [5] [6] [7] [8]

Documentation and Comments:

• Updated and clarified comments to indicate that only the endpoint is required and that the default endpoint will be used if not provided for GCS.

Minor Code Cleanups:

• Removed unnecessary newlines and improved formatting in test case definitions.

Bug Fixes:

• Fixed a logic error where a block was terminated with a semicolon instead of a brace in the GCS endpoint configuration.

Related Issue

Motivation and Context

Screenshots (if appropriate)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.42%. Comparing base (ce8ac11) to head (d646d4e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1753      +/-   ##
==========================================
- Coverage   46.63%   46.42%   -0.22%     
==========================================
  Files          87       87              
  Lines       24807    24692     -115     
==========================================
- Hits        11569    11463     -106     
+ Misses      13238    13229       -9     

Files with missing lines	Coverage Δ
dragonfly-client-backend/src/object_storage.rs	86.49% <100.00%> (-1.42%)	⬇️

... and 1 file with indirect coverage changes

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