fix: fix adding the node user

User adduser instead of useradd since the former isn't installed
in the base alpine image.

Add both a node user and group with 1000 id following the same
procedure as the official nodejs image.

https://github.com/nodejs/docker-node/blob/main/Dockerfile-alpine.template#L5

Dockerfile

@@ -30,7 +30,8 @@ RUN node install.js
 
 FROM base AS app
 
-RUN useradd -ms /bin/bash node
+RUN addgroup -g 1000 node \
+  && adduser -u 1000 -G node -s /bin/sh -D node
 
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