Adds ARG to adjust local base image (#339)

## Overview
The `Dockerfile` hardcodes `quay.io/pypa/manylinux2014_x86_64`, with this PR it can now be adjusted:

```
# macos development
docker image build --build-arg="MANYLINUX_BASE_IMAGE=quay.io/pypa/manylinux2014_aarch64" \
    -t fasttask-runner:0.0.11 .

docker image build --build-arg="MANYLINUX_BASE_IMAGE=quay.io/pypa/manylinux2014_x86_64" \
    -t fasttask-runner:0.0.11 .
```

## Upstream Changes
Should this change be upstreamed to OSS (flyteorg/flyte)? If not, please uncheck this box, which is used for auditing. Note, it is the responsibility of each developer to actually upstream their changes. See [this guide](https://unionai.atlassian.net/wiki/spaces/ENG/pages/447610883/Flyte+-+Union+Cloud+Development+Runbook/#When-are-versions-updated%3F).
- [ ] To be upstreamed to OSS

fasttask/worker/Dockerfile

@@ -3,7 +3,12 @@
 # If you are running with the cache run:
 # docker builder prune --filter type=exec.cachemount
 
-FROM quay.io/pypa/manylinux2014_x86_64 as build
+# If your Flyte is running on aarch64 (Apple Silicon), run:
+# docker image build \
+#    --build-arg="MANYLINUX_BASE_IMAGE=quay.io/pypa/manylinux2014_aarch64" \
+#    -t fasttask-runner:TAG .
+ARG MANYLINUX_BASE_IMAGE=quay.io/pypa/manylinux2014_x86_64
+FROM ${MANYLINUX_BASE_IMAGE} as build
 
 RUN curl https://sh.rustup.rs -sSf | sh -s -- --profile=minimal -y
 ENV PATH="/root/.cargo/bin:${PATH}"