Add kube-apiserver, kube-controller-manager, kube-scheduler and etcd to glossary. (#6600)

* Move master component definitions to glossary

* review comments

* Update controller.yaml

Making a trivial change to un-stuck Travis

* Update controller.yaml

Removing trivial change

_data/glossary/kube-scheduler.yaml

@@ -0,0 +1,13 @@
+id: kube-scheduler
+name: kube-scheduler
+full-link: /docs/reference/generated/kube-scheduler/
+aka:
+- scheduler
+tags:
+- architecture
+short-description: >
+  Component on the master that watches newly created pods that have no node assigned, and selects a node for them to run on.
+long-description: >
+  Factors taken into account for scheduling decisions include individual and collective resource requirements, 
+  hardware/software/policy constraints, affinity and anti-affinity specifications, data locality, inter-workload interference
+  and deadlines.