[BUG][MARKDOWN] Primitive Type not set to true for primitives on Models

[HieronymusLex]

Description

When using both the html and markdown doc generators, isPrimitiveType is set to false for model vars even if the var is a primitive type. This leads to dead links for primitive types e.g. https://github.com/OpenAPITools/openapi-generator/blob/master/samples/documentation/markdown/Models/ApiResponse.md

openapi-generator version

v4.2.3

Command line used for generation

openapi-generator generate -i ./definition.yaml -g markdown -o docs

Steps to reproduce

1. Download https://raw.githubusercontent.com/OAI/OpenAPI-Specification/master/examples/v3.0/petstore.yaml
2. Generate markdown docs from the downloaded Pet Store sample yaml i.e.

   openapi-generator generate -i petstore.yaml -o petapidocs -g markdown
   

3. View petapidocs/Models/Pet.md

Expected Result
Primitive types such as string, integer etc. should not link to an external file. The relevant part of the mustache template: {{#isPrimitiveType}}**{{dataType}}**{{/isPrimitiveType}} https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/markdown-documentation/model.mustache#L10

Actual Result
Primitive types all have dead links because isPrimitiveType is set to false in the template

Suggest a fix

My guess is that there is something wrong with how isPrimitiveType is set for model vars but unsure what the fix is yet. I'll keep looking

[joelstobart]

It would be good to have this resolved :)