build: add multi-arch image publishing

[googs1025]

Summary

• Add buildx build and push targets for linux/amd64 and linux/arm64 images.
• Update existing image workflows to build and push multi-arch images in separate steps.
• Make sandbox-manager and agent-runtime Dockerfiles honor TARGETOS/TARGETARCH.

Test Plan

• make -n docker-buildx-controller docker-buildx-manager docker-buildx-runtime docker-buildx-sandbox-gateway docker-buildx-traffic-extension
• make -n docker-pushx-controller docker-pushx-manager docker-pushx-runtime docker-pushx-sandbox-gateway docker-pushx-traffic-extension
• ruby -e 'require "yaml"; ARGV.each { |f| YAML.load_file(f); puts f }' .github/workflows/docker-image-agent-sandbox-controller.yml .github/workflows/docker-image-sandbox-manager.yml .github/workflows/docker-image-agent-runtime.yml .github/workflows/docker-image-sandbox-gateway.yml\n- git diff --check\n- rg -n "GOARCH=amd64|docker push openkruise|ppc64le|docker-image-traffic-extension" dockerfiles .github/workflows/docker-image-*.yml Makefile

[kruise-bot]

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[kruise-bot]

Welcome @googs1025! It looks like this is your first PR to openkruise/agents 🎉

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.79%. Comparing base (23dc332) to head (00a6e90).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #545   +/-   ##
=======================================
  Coverage   79.79%   79.79%           
=======================================
  Files         205      205           
  Lines       15369    15369           
=======================================
  Hits        12264    12264           
  Misses       2662     2662           
  Partials      443      443           

Flag	Coverage Δ
unittests	79.79% <ø> (ø)

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[googs1025]

@AiRanthem @furykerry /PTAL