[opt](cloud) Check object existence before explicit object deletion

[wyxxxcat]

What problem does this PR solve?

S3 DeleteObject is idempotent and can return success even when the target object does not exist. Because of this, explicit file deletion in cloud recycler could silently ignore missing objects.
This change makes explicit object deletion verify object existence before deleting by default, so missing files are surfaced as errors instead of being treated as successful deletes.

What changed?

• Added an object existence check before S3ObjClient::delete_object and AzureObjClient::delete_object.
• Updated S3Accessor::delete_file to propagate NOT_FOUND instead of treating it as success.
• Added ObjClientOptions::check_exists_before_delete so explicit batch file deletes can request existence validation.
• Added cloud config enable_delete_file_check_object_exists, defaulting to true, to allow disabling the extra HEAD request when needed.
• Kept recursive/prefix cleanup behavior idempotent by default to avoid breaking retry and concurrent recycler cleanup flows.
• Added DCHECK when the pre-delete HEAD check fails.
• Added unit coverage for the S3 delete existence-check config behavior.

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris.
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