feat: multi platform support

- use build platform argument
Signed-off-by: Lakshya Singh <lakshay.singh1108@gmail.com>

lightningd/Dockerfile

@@ -1,4 +1,7 @@
-FROM alpine:3.16 as builder
+# build stage for core lightning and clboss
+FROM --platform=${TARGETPLATFORM:-${BUILDPLATFORM}} alpine:3.18 as builder
+
+ARG TARGETPLATFORM
 
 WORKDIR /build
 
@@ -45,7 +48,9 @@ RUN git clone -b 2023-09-gnuc-version --recurse-submodules https://github.com/ks
     make -j $(nproc) && \
     make install
 
-FROM alpine:3.16 as runner
+# final stage with runtime dependencies and pkgs
+FROM --platform=${TARGETPLATFORM:-${BUILDPLATFORM}} alpine:3.18 as runner
+
 LABEL maintainer.0="Lakshya Singh (@king-11)" \
   maintainer.1="Dev Random (@devrandom01)"