add logs for external file download

[vivki]

Proposed changes

This PR adds logs for external file downloads. These are needed on the NGINXaaS side to generate events.

Agent V3 currently does log errors caused by failed file downloads, e.g.

apply error: failed to download file /etc/nginx/mycert.cert from projects/900024435491/secrets/valyria-secret/versions/latest: download failed with status code 401: no workload identity pool provider specified

With this current change, any download errors will also be logged with a standard failure message to be parsed by NGINXaaS:

2026-04-01T10:15:32.123Z ERROR Failed to download external file event_tag=ID-1310 location=http://naasproxy:49152/google_secret_manager/projects%2F219735614622%2Fsecrets%2Fvxu-key%2Fversions%2F1 err="connection timed out"

Additionally, a success log is added, to be parsed by NGINXaaS:

2026-04-01T10:15:33.456Z INFO Successfully downloaded external file event_tag=ID-1310 location=http://naasproxy:49152/google_secret_manager/projects%2F219735614622%2Fsecrets%2Fvxu-key%2Fversions%2F1 hash=a3f5b8c9d2e1f4a7b6c5d8e9f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0

No existing logs have been changed.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.07%. Comparing base (3d4cf59) to head (b0eb19a).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1577      +/-   ##
==========================================
+ Coverage   85.05%   85.07%   +0.01%     
==========================================
  Files         105      105              
  Lines       13680    13691      +11     
==========================================
+ Hits        11636    11647      +11     
  Misses       1529     1529              
  Partials      515      515              

Files with missing lines	Coverage Δ
internal/file/external_file_operator.go	80.20% <100.00%> (+0.52%)	⬆️
internal/file/file_manager_service.go	74.82% <100.00%> (+0.34%)	⬆️

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[vivki]

I have hereby read the F5 CLA and agree to its terms.

[vivki]

recheck

[vivki]

I have hereby read the F5 CLA and agree to its terms

[vivki]

recheck