Added detection for CoreOS devices (#8899)

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includes/definitions/coreos.yaml

@@ -0,0 +1,11 @@
+os: coreos
+type: server
+group: unix
+text: CoreOS
+icon: coreos
+processor_stacked: true
+over:
+    - { graph: device_processor, text: 'Processor Usage' }
+    - { graph: device_ucd_memory, text: 'Memory Usage' }
+discovery:
+    - sysDescr_regex: '/^Linux.*coreos/'