Restore maintainer label to container images

If we don't set this label, it's inherited from the base image. For UBI
images, the value is "Red Hat Inc", and Red Hat's preflight validation
complains about it.

changelog/fragments/1736520682-restore-maintainer-label.yaml

@@ -0,0 +1,32 @@
+# 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: bug-fix
+
+# Change summary; a 80ish characters long description of the change.
+summary: Restore `maintainer` label for container images
+
+# Long description; in case the summary is not enough to describe the change
+# this field accommodate a description without length limits.
+# NOTE: This field will be rendered only for breaking-change and known-issue kinds at the moment.
+#description:
+
+# Affected component; usually one of "elastic-agent", "fleet-server", "filebeat", "metricbeat", "auditbeat", "all", etc.
+component: elastic-agent
+
+# PR URL; 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: https://github.com/owner/repo/1234
+
+# Issue URL; 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: https://github.com/owner/repo/1234

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

@@ -110,6 +110,9 @@ LABEL \
   org.opencontainers.image.vendor="{{ .BeatVendor }}" \
   org.opencontainers.image.authors="infra@elastic.co" \
   name="{{ .BeatName }}" \
+  # The maintainer label is deprecated, but RedHat still checks for it in their preflight validation. If we don't set
+  # it here, we inherit it from the base image, and fail said validation.
+  maintainer="infra@elastic.co" \
   vendor="{{ .BeatVendor }}" \
   version="{{ beat_version }}{{if .Snapshot}}-SNAPSHOT{{end}}" \
   release="1" \