Multiarch docker GitHub actions (#2065)

## Issue Addressed

Resolves #1512

## Proposed Changes

- Adds a new docker Github Actions workflow  
- Removes the Dockerhub hook
- Adds a new Dockerfile for use with pre-existing cross-compiled binaries 
- on pushes to `unstable` 
  - builds an ARM64 image and tags it `latest-arm64-unstable`
  - builds an AMD64 image and tags it `latest-amd64-unstable`
  - builds an multiarch image by creating a manifest list referencing the prior two images and tags it `latest-unstable`
- on pushes to `stable` 
  - builds an ARM64 image and tags it `latest-arm64`
  - builds an AMD64 image and tags it `latest-amd64`
  - builds an multiarch image by creating a manifest list referencing the prior two images and tags it `latest`

## Additional Info
- for ARM64, first `cross` is used to cross compile the `lighthouse` and  `lcli` binaries, then `docker buildx` is installed to actually build the docker image for the correct target platform. The image build pretty much just copies the binaries from local into the docker image (thanks @michaelsproul :) )
- The AMD64 and ARM64 builds run in parallel, in total it's been taking around 45mins on a local runner
- This PR does **not** cover version tags on docker images at the moment

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

Dockerfile.cross

@@ -0,0 +1,10 @@
+# This image is meant to enable cross-architecture builds.
+# It assumes the lighthouse binary has already been
+# compiled for `$TARGETPLATFORM` and moved to `./bin`.
+FROM --platform=$TARGETPLATFORM debian:buster-slim
+RUN apt-get update && apt-get install -y --no-install-recommends \
+  libssl-dev \
+  ca-certificates \
+  && apt-get clean \
+  && rm -rf /var/lib/apt/lists/*
+COPY ./bin/lighthouse /usr/local/bin/lighthouse