Update Dockerfile to dynamically set architecture based on TARGETARCH for improved multi-architecture support

Dockerfile

@@ -1,11 +1,13 @@
 FROM alpine:latest
 
-# Set architecture as a build argument with a default value
-ARG ARCH=x86_64
-
 RUN apk add --no-cache wget ca-certificates tar
 
-RUN wget -q https://install.speedtest.net/app/cli/ookla-speedtest-1.2.0-linux-${ARCH}.tgz && \
+RUN if [ "$TARGETARCH" = "amd64" ]; then \
+    ARCH="x86_64"; \
+    elif [ "$TARGETARCH" = "arm64" ]; then \
+    ARCH="aarch64"; \
+    fi && \
+    wget -q https://install.speedtest.net/app/cli/ookla-speedtest-1.2.0-linux-${ARCH}.tgz && \
     tar -xzf ookla-speedtest-1.2.0-linux-${ARCH}.tgz -C /usr/bin && \
     rm ookla-speedtest-1.2.0-linux-${ARCH}.tgz && \
     chmod +x /usr/bin/speedtest