Add uptime CODEOWNER entries. (#63616)

Author: justinkambic

.github/CODEOWNERS

@@ -80,6 +80,8 @@
 /x-pack/legacy/plugins/ingest_manager/ @elastic/ingest-management
 /x-pack/plugins/observability/ @elastic/logs-metrics-ui @elastic/apm-ui @elastic/uptime @elastic/ingest-management
 /x-pack/legacy/plugins/monitoring/ @elastic/stack-monitoring-ui
+/x-pack/legacy/plugins/uptime @elastic/uptime
+/x-pack/plugins/uptime @elastic/uptime
 
 # Machine Learning
 /x-pack/legacy/plugins/ml/  @elastic/ml-ui