Add database CLIs to app images.

I dislike that this bloats the app images by another 50 MB or so, but
it's not a runtime overhead and it saves us from having to build and
it means we can just tell people to use `k exec deploy/foo -- rails db`
rather than having to write and maintain yet another wrapper script.

base.Dockerfile

@@ -107,7 +107,8 @@ ENV PATH=${TMPDIR_FOR_RUBY_WRAPPERS_DIR}:${PATH}
 
 # Install node.js, yarn and other runtime dependencies.
 COPY --from=builder /usr/share/keyrings/nodesource.gpg /usr/share/keyrings/
-RUN install_packages ca-certificates curl libjemalloc-dev libgdbm6 libyaml-0-2 libmariadb3 libpq5 tzdata; \
+RUN install_packages ca-certificates curl libjemalloc-dev libgdbm6 libyaml-0-2 \
+      libmariadb3 libpq5 mariadb-client postgresql-client tzdata; \
     echo "deb [signed-by=/usr/share/keyrings/nodesource.gpg] https://deb.nodesource.com/node_18.x jammy main" | tee /etc/apt/sources.list.d/nodesource.list; \
     install_packages nodejs; \
     echo -n node version:\ ; node -v; \