fix: Allow docker driver to properly use cache (#126)

This fix involves creating a new function for the `BuildDriver` trait
called `build_tag_push`. In order to get the proper logic in place to
make use of `docker buildx`, I had to create a separate function that
would construct the build command to include all of the tags necessary
for pushing. A default implementation of `build_tag_push` will be used
for `podman` and `buildah` which was originally from the build command's
functions. Now that we have custom logic for docker builds, we can take
advantage of using the GitHub cache features without having the `--load`
arg which had a big negative effect on build times. We can now also use
docker for creating local `oci-archive` tarballs for local rebasing.
Making use of the `oci-archive` will require the user to create a
`docker-container` builder as it is not supported on the standard
`docker` builder.

https://docs.docker.com/build/exporters/oci-docker/

.github/workflows/build-pr.yml

@@ -91,7 +91,6 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
         with:
-          driver: docker
           install: true
 
       - name: Earthly login
@@ -119,6 +118,7 @@ jobs:
           GH_TOKEN: ${{ github.token }}
           GH_PR_EVENT_NUMBER: ${{ github.event.number }}
           COSIGN_PRIVATE_KEY: ${{ secrets.TEST_SIGNING_SECRET }}
+          BB_BUILDKIT_CACHE_GHA: true
         run: |
           cd integration-tests/test-repo
           if [ -n "$GH_TOKEN" ] && [ -n "$COSIGN_PRIVATE_KEY" ]; then