simplify the Dockerfiles

- remove the caching, it's more trouble than it's worth
- use '&&' instead of ';', so it fails earlier

dockerfiles/alpine.Dockerfile

@@ -3,8 +3,6 @@ ARG BASE_REGISTRY="docker.io"
 
 FROM ${BASE_REGISTRY}/ruby:${RUBY_VERSION}-alpine AS base
 
-ARG TARGETARCH
-
 ENV RACK_ENV="production" \
   BUNDLE_DEPLOYMENT=true \
   BUNDLE_PATH="/usr/local/bundle" \
@@ -14,23 +12,21 @@ ENV RACK_ENV="production" \
 WORKDIR /kubernaut
 
 RUN \
-  --mount=type=cache,id=var-cache-apk-${TARGETARCH},target=/var/cache/apk,sharing=locked \
-  apk update -q; \
+  apk update -q && \
   apk add bash jemalloc
 
 FROM base AS build
 
 RUN \
-  --mount=type=cache,id=var-cache-apk-${TARGETARCH},target=/var/cache/apk,sharing=locked \
-  apk update -q; \
-  apk add musl-dev gcc make; \
+  apk update -q && \
+  apk add musl-dev gcc make && \
   apk add bash jemalloc
 
 COPY Gemfile Gemfile.lock ./
 
 RUN \
-  --mount=type=cache,id=usr-local-bundle-ruby-cache-${TARGETARCH},target=${BUNDLE_PATH}/ruby/3.4.0/cache,sharing=locked \
-  bundle install
+  bundle install && \
+  rm -rf ~/.bundle/ "${BUNDLE_PATH}"/ruby/*/cache "${BUNDLE_PATH}"/ruby/*/bundler/gems/*/.git
 
 COPY . .
 
@@ -39,7 +35,7 @@ FROM base
 ENV PORT=4567
 
 RUN \
-  addgroup --system --gid 666 kubernaut; \
+  addgroup --system --gid 666 kubernaut && \
   adduser --system --uid 666 --ingroup kubernaut --shell /bin/bash --disabled-password kubernaut
 
 COPY --from=build "${BUNDLE_PATH}" "${BUNDLE_PATH}"