fix(docker-build-push-image): pass builder name to docker/build-push-action

[ricky-undeadcoders]

Currently in docker-build-push-action we're not assigning a buildx builder when calling docker/build-push-action, so we're using a new builder instead of the one we setup using docker/setup-buildx. This resolves that by passing the builder name that we've created.

• Docker Buildx setup: Added an id (setup-buildx) to the Buildx setup step, allowing outputs from this step to be referenced in later steps.
• Docker Buildx usage: Updated the Docker build step to use the Buildx builder instance created earlier by referencing ${{ steps.setup-buildx.outputs.name }}.