ci: add pre-baked base image workflow

[tennix]

Summary

• Add Dockerfiles for pre-baked release-1.x CI base images:
  • backup-manager-base: PingCAP QE base + backup-manager external tools (rclone, shush) and required packages.
  • e2e-base: Debian bookworm + e2e tools (kubectl, helm, AWS CLI, cert-manager manifest) and required packages.
• Add CI Base Images workflow to build both images for linux/amd64,linux/arm64.
• The workflow validates base-image changes on PRs and can be manually dispatched to push immutable tags to GHCR.
• Document the image contents and publish/update policy.

Motivation

release-1.x CI/Prow flakes are mostly caused by downloading external binaries during normal Docker image builds. This PR adds the pre-baked image definitions and publish workflow first. After the images are published and verified pullable, a follow-up PR will update the existing Dockerfiles to consume the pre-baked images.

Validation

• git diff --check
• Built build/ci-images/backup-manager-base locally for linux/arm64 and verified the Dockerfile check step:
  • env -u RCLONE_VERSION rclone version
  • command -v shush
• Built build/ci-images/e2e-base locally for linux/arm64 and verified the Dockerfile check step:
  • kubectl version --client=true --output=yaml
  • helm version --short
  • aws --version
  • test -s /cert-manager.yaml

Follow-up

After this workflow publishes a stable tag, open a second PR to update:

• images/tidb-backup-manager/Dockerfile
• images/tidb-backup-manager/Dockerfile.e2e
• tests/images/e2e/Dockerfile

to use the published pre-baked images instead of downloading external binaries during normal CI/CD builds.

[ti-chi-bot]

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[ti-chi-bot]

@tennix: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-e2e-kind-dmcluster	00132c8	link	false	/test pull-e2e-kind-dmcluster
pull-e2e-kind-basic	00132c8	link	false	/test pull-e2e-kind-basic
pull-e2e-kind-serial	00132c8	link	false	/test pull-e2e-kind-serial
pull-e2e-kind-scale-simultaneously	00132c8	link	false	/test pull-e2e-kind-scale-simultaneously
pull-e2e-kind-tngm	00132c8	link	false	/test pull-e2e-kind-tngm

Full PR test history. Your PR dashboard.

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