Migrate to feature/s3/transfermanager

[taoki-ss]

feature/s3/manager is deprecated in favor of feature/s3/transfermanager.

• S3 Transfer Manager v2 Now Generally Available aws/aws-sdk-go-v2#3306

As the argument types of WithUploaderOptions() and WithDownloaderOptions() are changed, bump the major version to v3.
Go 1.23 is dropped since transfermanager requires Go 1.24.
Also add migration guide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.92%. Comparing base (4df4d36) to head (fa682e4).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #471      +/-   ##
==========================================
+ Coverage   81.88%   81.92%   +0.04%     
==========================================
  Files           5        5              
  Lines         414      415       +1     
==========================================
+ Hits          339      340       +1     
  Misses         45       45              
  Partials       30       30              

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[at-wat]

LGTM

[taoki-ss]

@at-wat Thank you for your review and approval.
Before merging, I would like to confirm two points regarding the release.

1. Would it be acceptable for me to merge this PR and tag v3.0.0 (including creating the GitHub Release)?
2. Would it be acceptable to release v3.0.0 directly, without release candidates?

[at-wat]

@taoki-ss

• Would it be acceptable for me to merge this PR and tag v3.0.0 (including creating the GitHub Release)?

Yes, please tidy up the commit message on squash merge.

• Would it be acceptable to release v3.0.0 directly, without release candidates?

Creating v3.0.0 directly would be fine if there are no other pending breaking changes and the current changes are confident enough.

[at-wat]

BTW, it's better to merge the pending dependency updates before creating the new release

[taoki-ss]

@at-wat Thank you for the confirmation.
I have merged the pending dependency updates (#468 and #469) before this PR, and released v3.0.0.
https://github.com/seqsense/s3sync/releases/tag/v3.0.0

The AWS SDK updates (#453, #458, #460 and #470) were already included in this PR and were closed automatically by Renovate, and #466 was superseded by #469.