Ensure protoc is installed for release CI (#3621)

## Issue Addressed

The release CI is currently broken due to the addition of the `protoc` dependency. Here's a failure of the release flow running on my fork: https://github.com/michaelsproul/lighthouse/actions/runs/3155541478/jobs/5134317334

## Proposed Changes

- Install `protoc` on Windows and Mac so that it's available for `cargo install`.
- Install an x86_64 binary in the Cross image for the aarch64 platform: we need a binary that runs on the host, _not_ on the target.
- Fix `macos` local testnet CI by using the Github API key to dodge rate limiting (this issue: https://github.com/actions/runner-images/issues/602).

scripts/cross/aarch64-unknown-linux-gnu.dockerfile

@@ -1,14 +0,0 @@
-ARG CROSS_BASE_IMAGE
-FROM $CROSS_BASE_IMAGE
-
-RUN apt-get update -y && apt-get upgrade -y
-
-RUN apt-get install -y unzip && \
-    PB_REL="https://github.com/protocolbuffers/protobuf/releases" && \
-    curl -L $PB_REL/download/v3.15.8/protoc-3.15.8-linux-aarch_64.zip -o protoc.zip && \
-    unzip protoc.zip -d /usr && \
-    chmod +x /usr/bin/protoc
-
-RUN apt-get install -y cmake clang-3.9
-
-ENV PROTOC=/usr/bin/protoc