DOC-13911: Migrate OpenAPI Generator templates to Handlebars (#206)

* Create handlebars templates
* Remove mustache templates
* Switch all gradle build scripts to use handlebars
* Get tag names from operation
* Two-column model ToC
* Output Nullable field
* Use "yes" for unique items and nullable
* Only show top-level models in the nav
* Update Analytics Links spec with nullable fields
* Fix Query Settings examples (jsonc → json)
* Get rid of the italics
* Handle Redocly x-enumDescriptions
* Use capitalize helper for tag names
* Update security schemas to use x-displayName
* Build output documentation

Author: simon-dew

docs/modules/analytics-rest-admin/analytics-admin.gradle

@@ -20,4 +20,5 @@ openApiGenerate {
             generateAliasAsModel: "true"
     ]
     generateAliasAsModel = true
+    engine = "handlebars"
 }

docs/modules/analytics-rest-admin/attachments/_analytics-admin.yaml

@@ -762,6 +762,7 @@ components:
 
  securitySchemes:
   AnalyticsManageAnalyticsSelect:
+    x-displayName: Analytics Manage / Analytics Select
     type: http
     scheme: basic
     description: |
@@ -775,6 +776,7 @@ components:
       * Analytics Admin
 
   ClusterReadPoolsRead:
+    x-displayName: Cluster Read / Pools Read
     type: http
     scheme: basic
     description: |
@@ -786,6 +788,7 @@ components:
       * Analytics Admin
 
   AnalyticsManage:
+    x-displayName: Analytics Manage
     type: http
     scheme: basic
     description: |