chore: use TOML config with buildx to avoid DockerHub rate limits

[lemeurherveCB]

This PR uses TOM config with buildx if executed on CI and if /etc/buildkitd.toml file exists to use registry mirrors.

Supersedes and closes #497

Similar to:

• chore: use TOML config with buildx to avoid DockerHub rate limits docker-agent#958

Ref:

• [ci.jenkins.io] Fix HTTP/429 DockerHub errors for buildx builder using docker-container jenkins-infra/helpdesk#4585 (comment)
• feat(jenkinscontroller) provides Docker buildX TOML setup to users jenkins-infra/jenkins-infra#3938
• https://docs.docker.com/build/buildkit/configure/#registry-mirror

Testing done

make docker-init + CI

Submitter checklist

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• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[dduportal]

LGTM!

Note: I've changed the title prefix of this PR from fix to choreas it does not change anything in the image.