feat: make npm install work with elastic-agent user

Author: pkoutsovasilis

dev-tools/packaging/templates/docker/Dockerfile.elastic-agent.tmpl

@@ -116,7 +116,7 @@ RUN set -e ; \
 
 COPY docker-entrypoint /usr/local/bin/docker-entrypoint
 RUN groupadd --gid 1000 {{ .BeatName }} && \
-    useradd -M --uid 1000 --gid 1000 --groups 0 {{ .user }} && \
+    useradd -M --uid 1000 --gid 1000 {{ .user }} && \
     chmod 755 /usr/local/bin/docker-entrypoint && \
     true
 
@@ -196,10 +196,13 @@ RUN cd {{$beatHome}}/.node \
   && chmod ugo+rwX -R $NODE_PATH \
 # Install synthetics as a regular user, installing npm deps as root odesn't work
    # fix .node .npm and .synthetics
-   && chown -R {{ .user }}:{{ .user }} $NODE_PATH
+   && chown -R {{ .user }}:{{ .user }} $NODE_PATH \
+   && mkdir -p {{ $beatHome }}/.npm/_logs \
+   && chown -R {{ .user }}:{{ .user }} {{ $beatHome }}/.npm \
+   && chown -R {{ .user }}:{{ .user }} {{ $beatHome }}/.cache
 USER {{ .user }}
 # If this fails dump the NPM logs
-RUN (npm i -g --loglevel verbose --engine-strict @elastic/synthetics@stack_release || sh -c 'tail -n +1 /root/.npm/_logs/* && exit 1') && \
+RUN (npm i -g --loglevel verbose --engine-strict @elastic/synthetics@stack_release || sh -c 'tail -n +1 {{ $beatHome }}/.npm/_logs/* && exit 1') && \
     chmod ugo+rwX -R $NODE_PATH
 USER root
 
@@ -218,7 +221,6 @@ RUN for iter in {1..10}; do \
 
 {{- end }}
 # root group no more for elastic-agent user
-RUN gpasswd --delete {{ .user }} root
 USER {{ .user }}