[Stack Monitoring] Switch cgroup memory fields to keyword (#88260)

Per https://www.elastic.co/guide/en/elasticsearch/reference/current/cluster-nodes-stats.html they should be strings.

docs/changelog/88260.yaml

@@ -0,0 +1,5 @@
+pr: 88260
+summary: "[Stack Monitoring] Switch cgroup memory fields to keyword"
+area: Monitoring
+type: bug
+issues: []

x-pack/plugin/core/src/main/resources/monitoring-es-mb.json

@@ -732,14 +732,16 @@
                                 "usage": {
                                   "properties": {
                                     "bytes": {
-                                      "type": "long"
+                                      "ignore_above": 1024,
+                                      "type": "keyword"
                                     }
                                   }
                                 },
                                 "limit": {
                                   "properties": {
                                     "bytes": {
-                                      "type": "long"
+                                      "ignore_above": 1024,
+                                      "type": "keyword"
                                     }
                                   }
                                 }