[BUG][scala-akka] generates a readme linking to model docs that don't exist

[ckipp01]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

While using scala-akka generator it seems impossible to get the model docs generated. For example, I followed the instructions similar to those in the WIKI to test this against the current master branch:

git clone https://github.com/openapitools/openapi-generator.git
cd openapi-generator
mvn clean install
java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
  -i modules/openapi-generator/src/test/resources/3_0/scala-akka/petstore.yaml \
  -o scala-test
  -g scala-akka

After doing this you'll see that there is a README.md created that has the following section:

## Documentation for Models

 - [ApiResponse](ApiResponse.md)
 - [Category](Category.md)
 - [Order](Order.md)
 - [Pet](Pet.md)
 - [Tag](Tag.md)
 - [User](User.md)

However, none of these model docs actually exist.

openapi-generator version

The last commit at the time of checking this is 158649a

OpenAPI declaration file content or url

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/test/resources/3_0/scala-akka/petstore.yaml

Generation Details

Just follow the steps up above in the description

Steps to reproduce

Just follow the steps up above in the description

Related issues/PRs

Not exactly sure if these are the same or related, but they all seems to have to do with scala-akka and doc generation not working as expected.

#8966
#5795

Suggest a fix

I'm pretty unfamiliar with how this is all supposed to work, so no idea.

[wing328]

Closed via the PR by @nMoncho

Please pull the latest master to give it another try.