fix: add v-prefixed GHCR image tags for release consistency

[hwan515]

Summary

• Add type=semver,pattern=v{{version}} to the container publish workflow
• This publishes both 0.55.1 and v0.55.1 tags to GHCR
• Fixes the inconsistency where GitHub Releases use v-prefixed tags but GHCR images don't

Problem

Users look at the Releases page and see v0.55.1, then naturally run:

docker pull ghcr.io/google/cadvisor:v0.55.1
# Error: not found

This has broken CI/CD pipelines (see #3856, #3712, #3807).

Change

One line added to .github/workflows/publish-container.yml:

type=semver,pattern=v{{version}}

This makes docker/metadata-action generate an additional tag with the v prefix, so both formats work.

Test plan

• For tag v0.55.1, the workflow will now generate:
  • 0.55.1 (existing, {{version}})
  • v0.55.1 (new, v{{version}})
  • 0.55 (existing, {{major}}.{{minor}})
  • latest
  • SHA-based tag

Fixes #3856

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[hwan515]

I have signed the Google CLA. Please re-check.

[hwan515]

/gclabot re-check