Add an Alpine Dockerfile build

This may be run with:

    ./docker/docker_run_tests.sh ./docker/alpine.Dockerfile

docker/alpine.Dockerfile

@@ -0,0 +1,27 @@
+FROM alpine:3.13
+
+ENV LANG C.UTF-8
+ENV LC_ALL C.UTF-8
+
+RUN apk add bash cmake g++ gettext-dev git libintl musl-dev ncurses-dev ninja python3 py3-pexpect
+
+RUN addgroup -g 1000 fishuser
+
+RUN adduser \
+    --disabled-password \
+    --gecos "" \
+    --home "/home/fishuser" \
+    --ingroup fishuser \
+    --uid 1000 \
+    fishuser
+
+RUN mkdir -p /home/fishuser/fish-build \
+  && mkdir /fish-source \
+  && chown -R fishuser:fishuser /home/fishuser /fish-source
+
+USER fishuser
+WORKDIR /home/fishuser
+
+COPY fish_run_tests.sh /
+
+CMD /fish_run_tests.sh