feat(fleet): collect Docker logs and metrics

Mirrors the behaviour of the Metricsbeat and Filebeat extensions through
Elastic Agent, using the Docker integration.

.github/workflows/scripts/run-tests-fleet.sh

@@ -35,7 +35,7 @@ endgroup
 #   AND event.dataset:"system.cpu"
 #   AND metricset.name:"cpu"
 #
-log 'Searching a document generated by Fleet Server'
+log 'Searching a system document generated by Fleet Server'
 
 declare response
 declare -i count
@@ -70,3 +70,44 @@ if (( count == 0 )); then
 	echo 'Expected at least 1 document'
 	exit 1
 fi
+
+# We expect to find log entries for the 'elasticsearch' Compose service using
+# the following query:
+#
+#   agent.name:"fleet-server"
+#   AND agent.type:"filebeat"
+#   AND container.name:"docker-elk-elasticsearch-1"
+#
+log 'Searching a container document generated by Fleet Server'
+
+response=
+count=0
+
+was_retried=0
+
+# retry for max 60s (30*2s)
+for _ in $(seq 1 30); do
+	response="$(curl "http://${ip_es}:9200/logs-docker.container_logs-default/_search?q=agent.name:%22fleet-server%22%20AND%20agent.type:%22filebeat%22%20AND%20container.name:%22docker-elk-elasticsearch-1%22&pretty" -s -u elastic:testpasswd)"
+
+	set +u  # prevent "unbound variable" if assigned value is not an integer
+	count="$(jq -rn --argjson data "${response}" '$data.hits.total.value')"
+	set -u
+
+	if (( count > 0 )); then
+		break
+	fi
+
+	was_retried=1
+	echo -n 'x' >&2
+	sleep 2
+done
+if ((was_retried)); then
+	# flush stderr, important in non-interactive environments (CI)
+	echo >&2
+fi
+
+echo "$response"
+if (( count == 0 )); then
+	echo 'Expected at least 1 document'
+	exit 1
+fi