Revert "Just always build latest docker images and let docker hub rej…

…ect duplicates"

This reverts commits:

	eef1eb1
	51b03df
	25b0792
	39aa169
	619d0db
	8f8bcb6

The current logic is flawed in that it always builds the latest commit
from the main branch and replaces the release tag on Docker Hub with it.

.buildkite/docker-image.yml

@@ -20,11 +20,10 @@ steps:
         .
   - wait
   - label: "🚀 Build & publish the release image to Docker Hub"
-    if: build.branch == "main"
+    if: build.tag =~ /@core\/sync-service@/
     command:
       - export ELECTRIC_IMAGE_NAME="${DOCKERHUB_REPO}/${IMAGE_NAME}"
       - cd ./packages/sync-service
-      - git fetch --tags
       - export ELECTRIC_VERSION=$(jq '.version' -r package.json)
       - docker buildx build --platform linux/arm64/v8,linux/amd64 --push
         --build-arg ELECTRIC_VERSION=$${ELECTRIC_VERSION}