feat(docker): enhance base image mirroring process and update documentation

- Updated `mirror-base-images.sh` to skip existing tags in Gitea and retry on 429 errors, improving efficiency and reducing unnecessary requests.
- Modified CI workflow to utilize a temporary environment file for mirrored base images, ensuring better handling of existing images.
- Enhanced README documentation to reflect changes in the mirroring process and clarify the behavior when tags already exist.

.gitea/workflows/cd.yaml

@@ -108,10 +108,9 @@ jobs:
           password: ${{ secrets.ACTIONS_PAT }}
       - name: Mirror base images into buildcache
         if: steps.rel.outputs.released == 'true'
-        id: mirror
-        continue-on-error: true
         env:
           REGISTRY: git.shx.one/${{ steps.meta.outputs.owner_lc }}
+          MIRROR_ENV_FILE: ${{ runner.temp }}/mirror-base.env
         run: sh deploy/docker/mirror-base-images.sh
       - name: Build and push images (bake)
         if: steps.rel.outputs.released == 'true'
@@ -126,16 +125,14 @@ jobs:
           CACHE_REF_WEB: git.shx.one/${{ steps.meta.outputs.owner_lc }}/evobgp-buildcache:web-buildcache
           CACHE_REF_BIRDC: git.shx.one/${{ steps.meta.outputs.owner_lc }}/evobgp-buildcache:birdc-buildcache
           BUILDX_BAKE_ENTITLEMENTS_FS: "0"
+          MIRROR_ENV_FILE: ${{ runner.temp }}/mirror-base.env
         run: |
           set -euxo pipefail
-          cache="git.shx.one/${{ steps.meta.outputs.owner_lc }}/evobgp-buildcache"
-          if [ "${{ steps.mirror.outcome }}" = "success" ]; then
-            export BASE_GOLANG="${cache}:base-golang-1.24-alpine"
-            export BASE_DEBIAN="${cache}:base-debian-bookworm-slim"
-            export BASE_NODE="${cache}:base-node-22-alpine"
-            export BASE_NGINX="${cache}:base-nginx-1.27-alpine"
-            export BASE_UBUNTU="${cache}:base-ubuntu-noble"
-            export BASE_DISTROLESS="${cache}:base-distroless-static-debian12-nonroot"
+          if [ -f "${MIRROR_ENV_FILE}" ]; then
+            set -a
+            # shellcheck disable=SC1090
+            . "${MIRROR_ENV_FILE}"
+            set +a
           fi
           docker buildx bake --allow=fs.read="${{ github.workspace }}" \
             -f deploy/docker/docker-bake.hcl default --push