[DOCS] Fix links to ES upgrade docs (elastic#5347) (elastic#5365)

Co-authored-by: Peter Brachwitz <peter.brachwitz@gmail.com>
(cherry picked from commit c8c84da)

# Conflicts:
#	docs/orchestrating-elastic-stack-applications/elasticsearch/orchestration.asciidoc

docs/design/0009-pod-reuse-es-restart.md

@@ -207,5 +207,5 @@ Chosen option: option 1, because that's the only one we have here? :)
 
 * [https://github.com/elastic/cloud-on-k8s/issues/454] Full cluster restart issue
 * [https://github.com/elastic/cloud-on-k8s/issues/453] Basic license support issue
-* [https://www.elastic.co/guide/en/elasticsearch/reference/current/restart-upgrade.html] Elasticsearch full cluster restart upgrade
-* [https://www.elastic.co/guide/en/elasticsearch/reference/current/rolling-upgrades.html] Elasticsearch rolling cluster restart upgrade
+* [https://www.elastic.co/guide/en/elasticsearch/reference/7.17/restart-upgrade.html] Elasticsearch full cluster restart upgrade
+* [https://www.elastic.co/guide/en/elasticsearch/reference/7.17/rolling-upgrades.html] Elasticsearch rolling cluster restart upgrade

docs/orchestrating-elastic-stack-applications/elasticsearch/orchestration.asciidoc

@@ -125,7 +125,7 @@ ECK migrates data away from the Elasticsearch nodes due to be removed and then d
 ECK migrates data away from the Elasticsearch nodes in the NodeSet and removes the underlying StatefulSet.
 * The specification of an existing NodeSet is updated. For example, the Elasticsearch configuration, or the PodTemplate resources requirements.
 +
-ECK performs a rolling upgrade of the corresponding Elasticsearch nodes. It follows the link:https://www.elastic.co/guide/en/elasticsearch/reference/current/rolling-upgrades.html[Elasticsearch rolling upgrade best practices] to update the underlying Pods while maintaining the availability of the Elasticsearch cluster where possible. In most cases, the process simply involves restarting Elasticsearch nodes one-by-one. Note that some cluster topologies may be impossible to deploy without making the cluster unavailable (see <<{p}-orchestration-limitations>> ).
+ECK performs a rolling upgrade of the corresponding Elasticsearch nodes. It follows the link:{stack-ref}/upgrading-elasticsearch.html[Elasticsearch rolling upgrade best practices] to update the underlying Pods while maintaining the availability of the Elasticsearch cluster where possible. In most cases, the process simply involves restarting Elasticsearch nodes one-by-one. Note that some cluster topologies may be impossible to deploy without making the cluster unavailable (see <<{p}-orchestration-limitations>> ).
 * An existing NodeSet is renamed.
 +
 ECK creates a new NodeSet with the new name, migrates data away from the old NodeSet, and then removes it. During this process the Elasticsearch cluster could temporarily have more nodes than normal. The Elasticsearch <<{p}-update-strategy,update strategy>> controls how many nodes can exist above or below the target node count during the upgrade.