Service Catalog docs (#5867)

* Service Catalog docs (+16 squashed commits)
Squashed commits:
[765e81d] rework install-service-catalog.md
[d81f799] tweak diagrams
[b7a3da7] Add tooltips
[3b256c5] more rework
[828000e] architecture diagram redux
[0b809d5] rework
[7829301] Outline provision-bind-external-service.md w/ filler text
[144fbb3] install service catalog v1
[47b5be4] Reorder images and bullet points
[fb577ae] Update What's Next links
[8ac984c] Include snippet for install and provision docs
[c2eeece] Add Install Service Catalog doc
[a84df64] Add hard line break
[7fb12c6] Add task
[75c46d3] Add List, Provision, and Bind diagrams
[6386feb] Service Catalog concept doc

* Add install-service-catalog-using-helm

* switch mysql examples to message queuing instead

* Incorporate feedback

* incorporate additional feedback

* Incorporate tech review feedback

_data/concepts.yml

@@ -33,6 +33,7 @@ toc:
     - docs/concepts/cluster-administration/network-plugins.md
     - docs/concepts/cluster-administration/device-plugins.md
     - docs/concepts/cluster-administration/sysctl-cluster.md
+  - docs/concepts/service-catalog/index.md
 
 - title: Containers
   section: