Change maintainer label to opencontainers in Dockerfile (#5527)

* Change maintainer label to opencontainers in Dockerfile

The old way of specifying maintainers in a Dockerfile was to use the
MAINTAINER instruction. This is now deprecated and the maintainer label was
used instead.

Nowadays the recommended way to set a maintainer is through the
`org.opencontainers.image.authors` label.

See https://docs.docker.com/reference/build-checks/maintainer-deprecated/.

* add changelog entry

changelog/fragments/1726238750-change-deprecated-maintainer-label-in-Dockerfile-to-org.opencontainers.image.authors.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: other
+
+# Change summary; a 80ish characters long description of the change.
+summary: change deprecated maintainer label in Dockerfile to org.opencontainers.image.authors
+
+# 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/elastic/elastic-agent/pull/5527
+
+# 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

@@ -108,8 +108,8 @@ LABEL \
   org.opencontainers.image.licenses="{{ .License }}" \
   org.opencontainers.image.title="{{ .BeatName | title }}" \
   org.opencontainers.image.vendor="{{ .BeatVendor }}" \
+  org.opencontainers.image.authors="infra@elastic.co" \
   name="{{ .BeatName }}" \
-  maintainer="infra@elastic.co" \
   vendor="{{ .BeatVendor }}" \
   version="{{ beat_version }}{{if .Snapshot}}-SNAPSHOT{{end}}" \
   release="1" \