Create observability CODEOWNERS reference (#57109)

* Create observability CODEOWNERS reference

* Update elastic/epm to elastic/ingest per Jen's request :)

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

.github/CODEOWNERS

@@ -69,9 +69,11 @@
 # Canvas
 /x-pack/legacy/plugins/canvas/  @elastic/kibana-canvas
 
-# Logs & Metrics UI
+# Observability UIs
 /x-pack/legacy/plugins/infra/ @elastic/logs-metrics-ui
+/x-pack/plugins/infra/ @elastic/logs-metrics-ui
 /x-pack/legacy/plugins/integrations_manager/ @elastic/epm
+/x-pack/plugins/observability/ @elastic/logs-metrics-ui @elastic/apm-ui @elastic/uptime @elastic/ingest
 
 # Machine Learning
 /x-pack/legacy/plugins/ml/  @elastic/ml-ui