build: fix make release-docker (#918)

PR
- https://github.com/zrepl/zrepl/pull/913

didn't update the `release-docker` flow to use `uv`, thereby breaking
it.

## Changes

- Create `.uv-version` file to centralize UV version between Dockerfile
and CircleCI
- Update build container to use `uv`

While at it, make life with the build container better:
- Create `zrepl_build` user in the build container as same UID/GID as
the caller of `make release-docker`
- Allow Ctrl-C to cancel `make release-docker` in interactive shells

build/build.Dockerfile

@@ -1,22 +1,30 @@
 FROM !SUBSTITUTED_BY_MAKEFILE
 
-RUN apt-get update && apt-get install -y \
-    python3-pip \
-    python3-venv \
-    unzip \
-    gawk
+ARG BUILD_UID=1000
+ARG BUILD_GID=1000
 
-# setup venv for docs
-ENV VIRTUAL_ENV=/opt/venv
-RUN python3 -m venv $VIRTUAL_ENV
-ENV PATH="$VIRTUAL_ENV/bin:$PATH"
-ADD docs/requirements.txt /tmp/requirements.txt
-RUN pip3 install -r /tmp/requirements.txt
+RUN apt-get update && apt-get install -y \
+    python3 \
+    unzip \
+    gawk \
+    curl
+
+# Create build user with the host's UID/GID before installing uv
+RUN groupadd -g ${BUILD_GID} zrepl_build && \
+    useradd -u ${BUILD_UID} -g ${BUILD_GID} -m zrepl_build
 
 # Go toolchain uses xdg-cache
 RUN mkdir -p /.cache && chmod -R 0777 /.cache
 
+# Install uv as the build user - version from .uv-version file
+ADD .uv-version /tmp/.uv-version
+USER zrepl_build
+RUN UV_VERSION=$(cat /tmp/.uv-version) && \
+    curl -LsSf https://astral.sh/uv/${UV_VERSION}/install.sh | sh
+
 # Go devtools are managed by Makefile
 
 WORKDIR /src
+ENV PATH="/home/zrepl_build/.local/bin:$PATH" \
+    GOCACHE="/.cache/go-build"