Add build script, fix awk -> gawk

docker/nwaku/v0.31.1/Dockerfile

@@ -1,3 +1,3 @@
 FROM wakuorg/nwaku:v0.31.1
-RUN apk add curl awk
+RUN apk add curl gawk
 

docker/nwaku/v0.31.1/build.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+# Create a new builder instance if it doesn't exist
+docker buildx create --name multiarch --node multiarch0 --use
+
+# Build and push the multi-architecture image
+docker buildx build --platform linux/amd64,linux/arm64 \
+  -t zorlin/nwaku:v0.31.1 \
+  -f Dockerfile \
+  --push .