docker: fix jq/python/pip installs (#1141)

packaging/rtx/Dockerfile

@@ -1,25 +1,33 @@
+# syntax=docker/dockerfile:1
 FROM rust as builder
 LABEL maintainer="jdx"
-SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 
+WORKDIR /usr/src/rtx
+COPY . /usr/src/rtx/
+RUN cargo build --release
+
+FROM rust as runtime
+
+SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 ENV RTX_DATA_DIR="/rtx"
 ENV RTX_CONFIG_DIR="/rtx"
 ENV RTX_CACHE_DIR="/rtx/cache"
 ENV PATH="/rtx/shims:$PATH"
-WORKDIR /usr/src/rtx
 
-COPY . /usr/src/rtx/
+COPY --from=builder /usr/src/rtx/target/release/rtx /usr/local/bin/rtx
 
-RUN cargo build --release \
-  && ln -s /usr/bin/{python3,python} \
-  && python -V \
-  && apt-get update && apt-get install -y \
+RUN <<EOT
+set -euxo pipefail
+
+apt-get update && apt-get install -y \
     jq \
-    && rm -rf /var/lib/apt/lists/* && apt-get clean
+    python3-pip
+rm -rf /var/lib/apt/lists/* && apt-get clean
 
-FROM rust as runtime
+ln -s ./python3 /usr/bin/python
 
-COPY --from=builder /usr/src/rtx/target/release/rtx /usr/local/bin/rtx
+rtx -v
+EOT
 
 WORKDIR /rtx
 ENTRYPOINT ["rtx"]