Automate docker version tag (#2150)

## Issue Addressed

N/A

## Proposed Changes

On any tag formatted `v*`, a full multi-arch docker build will be kicked off and automatically pushed to docker hub with the version tag.

This is a bit repetitive, because the image built will usually be the same as the image built on pushes to `stable`, but it seems like the simplest way to go about it and this will also work if we incorporate a workflow with `vX.X.X-rc` tags. 

## Additional Info

This may also need to wait for env variable updates: https://github.com/sigp/lighthouse/pull/2135#issuecomment-754977433

Co-authored-by: realbigsean <seananderson33@gmail.com>

.github/workflows/docker.yml

@@ -31,15 +31,10 @@ jobs:
             - name: Dockerhub login
               run: |
                   echo "${DOCKER_PASSWORD}" | docker login --username ${DOCKER_USERNAME} --password-stdin
-            - uses: actions-rs/toolchain@v1
-              with:
-                  toolchain: stable
             - name: Cross build lighthouse binary
-              uses: actions-rs/cargo@v1
-              with:
-                  use-cross: true
-                  command: build
-                  args: --release --manifest-path lighthouse/Cargo.toml --target aarch64-unknown-linux-gnu --features portable
+              run:  |
+                  cargo install cross
+                  make build-aarch64-portable
             - name: Move cross-built ARM binary into Docker scope
               run: |
                   mkdir ./bin;