Elastic agent counterpart of elastic/beats#33362 (#1528)

Always use the stack_release label for npm i

No changelog necessary since there are no user-visible changes

This lets us ensure we've carefully reviewed and labeled the version of the @elastic/synthetics NPM library that's bundled in docker images

(cherry picked from commit d2c780b)

changelog/fragments/1665784342-use-stack-version-npm-synthetics.yaml

@@ -0,0 +1,31 @@
+# Kind can be one of:
+# - breaking-change: a change to previously-documented behavior
+# - deprecation: functionality that is being removed in a later release
+# - bug-fix: fixes a problem in a previous version
+# - enhancement: extends functionality but does not break or fix existing behavior
+# - feature: new functionality
+# - known-issue: problems that we are aware of in a given version
+# - security: impacts on the security of a product or a user’s deployment.
+# - upgrade: important information for someone upgrading from a prior version
+# - other: does not fit into any of the other categories
+kind: feature
+
+# Change summary; a 80ish characters long description of the change.
+summary: use-stack-version-npm-synthetics
+
+# Long description; in case the summary is not enough to describe the change
+# this field accommodate a description without length limits.
+description: Always npm i the stack_release version of @elastic/synthetics
+
+# Affected component; a word indicating the component this changeset affects.
+component: synthetics-integration
+
+# PR number; optional; the PR number that added the changeset.
+# If not present is automatically filled by the tooling finding the PR where this changelog fragment has been added.
+# NOTE: the tooling supports backports, so it's able to fill the original PR number instead of the backport PR number.
+# Please provide it if you are adding a fragment for a different PR.
+pr: 1528
+
+# Issue number; optional; the GitHub issue related to this changeset (either closes or is part of).
+# If not present is automatically filled by the tooling with the issue linked to the PR number.
+#issue: 1234

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

@@ -191,7 +191,7 @@ RUN cd {{$beatHome}}/.node \
 RUN chown -R {{ .user }} $NODE_PATH
 USER {{ .user }}
 # If this fails dump the NPM logs
-RUN npm i -g --loglevel verbose -f @elastic/synthetics || sh -c 'tail -n +1 /root/.npm/_logs/* && exit 1'
+RUN npm i -g --loglevel verbose -f @elastic/synthetics@stack_release || sh -c 'tail -n +1 /root/.npm/_logs/* && exit 1'
 RUN chmod ug+rwX -R $NODE_PATH 
 USER root
 

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

@@ -181,7 +181,7 @@ RUN cd /usr/share/heartbeat/.node \
   && mkdir -p node \
   && curl ${NODE_DOWNLOAD_URL} | tar -xJ --strip 1 -C node \
   && chmod ug+rwX -R $NODE_PATH \
-  && npm i -g -f @elastic/synthetics && chmod ug+rwX -R $NODE_PATH
+  && npm i -g -f @elastic/synthetics@stack_release && chmod ug+rwX -R $NODE_PATH
 {{- end }}
 
 {{- range $i, $port := .ExposePorts }}