chore: add support for user agent in s3client

[remyleone]

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Relates OR Closes #0000

Release note for CHANGELOG:

[Copilot]

Pull request overview

This PR aims to add a custom User-Agent entry to the AWS SDK v2 S3 client used by the object namespace, so S3 traffic can be attributed to the CLI and its version.

Changes:

• Extracts BuildInfo from context in newS3Client.
• Adds an AWS SDK API middleware to append a User-Agent key/value to S3 requests.
• Wires the middleware through s3.Options.APIOptions.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.10%. Comparing base (e096674) to head (82a18d6).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5389   +/-   ##
=======================================
  Coverage   51.10%   51.10%           
=======================================
  Files         323      323           
  Lines       75301    75309    +8     
=======================================
+ Hits        38480    38488    +8     
  Misses      35350    35350           
  Partials     1471     1471           

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