Add hasReadOnly property to CodegenModel

[kota65535]

This PR adds the hasReadOnly property to CodegenModel when it has at least one read-only property.

Motivation

I ran into the same problem as #4190 with typescript-fetch generator. One solution can be using Omit to exclude read-only properties.

Given the following the OpenAPI schema and operation definition.

title: Task
type: object
properties:
  id:
    type: integer
    readOnly: true
  title:
    type: string

post:
  operationId: createTask
  requestBody:
    required: true
    content:
      application/json:
        schema:
          $ref: Task.yml
...

typescript-fetch generator generates the following code, which always requires an id property on request. But we don't need an id when creating a resource.

export interface CreateTaskRequest {
    task: Task;
}

With hasReadOnly property, we can rewrite the template like this...

{{#hasReadOnly}}Omit<{{{dataType}}}, {{#readOnlyVars}}'{{baseName}}'{{^-last}}|{{/-last}}{{/readOnlyVars}}>{{/hasReadOnly}}{{^hasReadOnly}}{{{dataType}}}{{/hasReadOnly}};

Then it will be rendered as follows.

export interface CreateTaskRequest {
    task: Omit<Task, 'id'>;
}

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh ./bin/configs/*.yaml
  ./bin/utils/export_docs_generators.sh
  

  (For Windows users, please run the script in Git BASH)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.1.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

[wing328]

lgtm. thanks for the enhancement

cc @OpenAPITools/generator-core-team