chore: improve Dockerfile to build as extension image

Some improvements were made to the Dockerfile to build using meson
and use a scratch image to have an extension image compatible
with CloudNativePG

Closes #10

Signed-off-by: Jonathan Gonzalez V. <jonathan.abdiel@gmail.com>

Author: sxd

docker/Dockerfile

@@ -1,29 +1,21 @@
-# syntax=docker/dockerfile:1.7
-FROM postgres:18 AS builder
+ARG BASE=ghcr.io/cloudnative-pg/postgresql:18-standard-trixie
+
+FROM $BASE AS builder
 ARG DEBIAN_FRONTEND=noninteractive
+USER root
 RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
     set -eux; \
     apt-get update; \
     apt-get install -y --no-install-recommends \
     build-essential \
     meson \
     libcurl4-openssl-dev \
-    postgresql-server-dev-18; \
-WORKDIR /work
-COPY . .
-RUN meson setup build && meson build -C build/
+    postgresql-server-dev-18
+WORKDIR /srv
+COPY meson.build LICENSE ./
+COPY src/ ./src/
+RUN meson setup build && meson compile -C build/
 
-FROM ghcr.io/cloudnative-pg/postgresql:18-standard-trixie
-ARG DEBIAN_FRONTEND=noninteractive
-USER root
-RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
-    set -eux; \
-    apt-get update; \
-    apt-get install -y --no-install-recommends libcurl4 ca-certificates; \
-    apt-get clean; \
-    rm -rf /var/lib/apt/lists/*
-COPY --chmod=0644 docker/certs/server.crt /usr/local/share/ca-certificates/kc-root.crt
-RUN update-ca-certificates
-ENV CURL_CA_BUNDLE=/etc/ssl/certs/ca-certificates.crt
-USER postgres
-COPY --from=builder /work/build/kc_validator.so /usr/lib/postgresql/18/lib/
+FROM scratch
+
+COPY --from=builder /srv/build/kc_validator.so /share/extension/