[glossary] Glossary MVP (#4865)

* [glossary] Glossary MVP

* resolve conflict

* initial pass at includable glossary data

* tag to term mapping

* Change StatefulSets to singular, StatefulSet

* revise glossary style guide, move

* make descriptions plural

_includes/templates/glossary/_error.md

@@ -0,0 +1,10 @@
+### ERROR: You must define a <span style="font-family: monospace">`{{ include.missing_block }}`</span> field
+{: style="color:red" }
+
+The glossary template requires that you provide text that {{ include.purpose }}.
+
+To get rid of this message and take advantage of this template, define the `{{ include.missing_block }}`
+field for the `{{ include.term }}` glossary term and populate it with content.
+
+See `_data/glossary/_example.yml` for reference.
+<!-- TEMPLATE_ERROR -->