Retry flaky Docker registry push during release publish

[devops-rob]

Summary

Release publish failed on a transient Docker Hub timeout, not a credentials or image problem:

Published docker.io/nomatronio/derrick:0.11.4
Created manifest list docker.io/nomatronio/derrick:latest
failed to put manifest .../latest: Get "https://auth.docker.io/token?...": net/http: request canceled (Client.Timeout exceeded while awaiting headers)

The versioned tag (0.11.4) and manifest were published successfully; only the :latest manifest push failed while re-authenticating with Docker Hub.

Fix

Add exponential backoff retries (default 5 attempts, 4s initial delay) around docker push and docker manifest push in .github/scripts/publish_docker_registries.sh.

Change Classification

• Open-core MPL files only (derrick)
• New public files only (no MPL-covered modifications)

Test Plan

• Script change only; will be exercised on next build workflow run on main.
• Re-running the failed workflow may also succeed without this change, but retries make publish resilient to Docker Hub auth flakiness.