Add new Plantuml generator for creating a schema diagram (#6255)

* add scaffolded new documentation generator files

* add openapi3 plantuml bin scripts

* change plantuml codegen to only generate a schemas.plantuml file

* initial plantuml schema diagram

* add item type to Lists

* add inheritance relationships

* add list one-to-many relationships

* add newline between model definitions and relationships

* add composition data type relationship

* remove allOf models and interface references

* add new entities data to SupportingFileData

* add List dataType support to entity fields

* remove composed types and remove allOf suffix from inline types

* add inheritances to supporting files data object

* add aggregation relationships to supporting file data

* add isList to compisition relationships

* refactor PlantumlDocumentationCodegenTest

* add property name to relationships

* remove old code form PlantumlDocumentationCodegen

* add plantuml generator sample output

* remove use of javafx.util.Pair

* fix casing of complex data type for fields

* add plantuml generator docs

* fix bug caused by assumption that inline _allOf types will always be unique but apparently they can be shared if they have identical properties!

* fix bug with missing relationships caused by shared identical _allOf schemas

Co-authored-by: Patrick.Burls <patrick.burls@bskyb.com>

samples/documentation/petstore/plantuml/.openapi-generator-ignore

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+# OpenAPI Generator Ignore
+# Generated by openapi-generator https://github.com/openapitools/openapi-generator
+
+# Use this file to prevent files from being overwritten by the generator.
+# The patterns follow closely to .gitignore or .dockerignore.
+
+# As an example, the C# client generator defines ApiClient.cs.
+# You can make changes and tell OpenAPI Generator to ignore just this file by uncommenting the following line:
+#ApiClient.cs
+
+# You can match any string of characters against a directory, file or extension with a single asterisk (*):
+#foo/*/qux
+# The above matches foo/bar/qux and foo/baz/qux, but not foo/bar/baz/qux
+
+# You can recursively match patterns against a directory, file or extension with a double asterisk (**):
+#foo/**/qux
+# This matches foo/bar/qux, foo/baz/qux, and foo/bar/baz/qux
+
+# You can also negate patterns with an exclamation (!).
+# For example, you can ignore all files in a docs folder with the file extension .md:
+#docs/*.md
+# Then explicitly reverse the ignore rule for a single file:
+#!docs/README.md
+
+#*.plantuml

samples/documentation/petstore/plantuml/.openapi-generator/VERSION

@@ -0,0 +1 @@
+5.0.0-SNAPSHOT

samples/documentation/petstore/plantuml/schemas.plantuml

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+@startuml
+
+title OpenAPI Petstore Schemas Diagram
+
+entity ApiResponse { 
+    code: Integer
+    type: String
+    message: String
+}
+
+entity Category { 
+    id: Long
+    name: String
+}
+
+entity Order { 
+    id: Long
+    petId: Long
+    quantity: Integer
+    shipDate: Date
+    status: String
+    complete: Boolean
+}
+
+entity Pet { 
+    id: Long
+    category: Category
+    * name: String
+    * photoUrls: List<String>
+    tags: List<Tag>
+    status: String
+}
+
+entity Tag { 
+    id: Long
+    name: String
+}
+
+entity User { 
+    id: Long
+    username: String
+    firstName: String
+    lastName: String
+    email: String
+    password: String
+    phone: String
+    userStatus: Integer
+}
+
+
+Pet -- Category : category
+Pet -- "0..*" Tag : tags
+
+@enduml