Update CODEOWNERS with separate Stack Monitoring team (#104828)

Adds [stack-monitoring](https://github.com/orgs/elastic/teams/stack-monitoring) and removes `@elastic/infra-monitoring-ui` (as being decommissioned), to review Stack Monitoring changes.

Author: paulb-elastic

.github/CODEOWNERS

@@ -3,18 +3,18 @@
 # For more info, see https://help.github.com/articles/about-codeowners/
 
 # Stack Monitoring index templates
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-alerts-7.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-beats-mb.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-beats.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-ent-search-mb.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-es-mb.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-es.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-kibana-mb.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-kibana.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-logstash-mb.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-logstash.json @elastic/infra-monitoring-ui
-x-pack/plugin/core/template-resources/src/main/resources/monitoring-mb-ilm-policy.json @elastic/infra-monitoring-ui
-x-pack/plugin/monitoring/src/main/java/org/elasticsearch/xpack/monitoring/MonitoringTemplateRegistry.java @elastic/infra-monitoring-ui
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-alerts-7.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-beats-mb.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-beats.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-ent-search-mb.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-es-mb.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-es.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-kibana-mb.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-kibana.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-logstash-mb.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-logstash.json @elastic/stack-monitoring
+x-pack/plugin/core/template-resources/src/main/resources/monitoring-mb-ilm-policy.json @elastic/stack-monitoring
+x-pack/plugin/monitoring/src/main/java/org/elasticsearch/xpack/monitoring/MonitoringTemplateRegistry.java @elastic/stack-monitoring
 
 # Fleet
 x-pack/plugin/fleet/src/main/java/org/elasticsearch/xpack/fleet @elastic/fleet