[REQ] consistent path formats in generated outputs for linux and windows

Background for the issue

Running

openapi-generator generate \
  --skip-validate-spec \
  --input-spec "schemas/algorithms.yaml" \
  --generator-name markdown \
  --output "docs/@api/algorithms"

on e.g.

# schemas/algorithms.yaml
openapi: 3.0.3
info:
  version: 0.0.0
  title: "Test models"
servers:
  - url: "https://myapi.acme.org"
paths: {}
components:
  schemas:
    AlgorithmModes:
      type: string
      enum:
        - RANDOM
        - GRADIENT
        - DEFAULT

yields the files

docs
├── @api
│   ├── algorithms
│   │   ├── Models
│   │   │   ├── AlgorithmModes.md
│   │   └── README.md

where the README.md file looks like

# Documentation for Test models

<a name="documentation-for-api-endpoints"></a>
## Documentation for API Endpoints

All URIs are relative to *https://myapi.acme.org*

Class | Method | HTTP request | Description
------------ | ------------- | ------------- | -------------


<a name="documentation-for-models"></a>
## Documentation for Models

 - [ClientConfig](.//Models/AlgorithmModes.md)


<a name="documentation-for-authorization"></a>
## Documentation for Authorization

All endpoints do not require authorization.

The issue

The issue is that the this output is generated in a way that depends on the operating system. The link

.//Models/AlgorithmModes.md

is generated with the standard path separator (.//) when running on linux/osx. But when running on windows, the non-standard ./\ path separator is used.

This is particularly irksome when using this tool in a repository maintained by multiple developers some on windows, some on linux/osx.

Describe the solution you'd like

Either forcibly ensure that .// is always used. Or provide a new flag, e.g.

--path-root-format [linux|windows|system]
# linux: uses ".//" regardless of the system on which the tool is run
# windows: uses "./\" regardless of the system on which the tool is run
# system: uses ".//" or "./\" dependent upon the system on which the tool is run

for backwards compatibility, one could make --path-root-format system the default, but even here it may be better to make --path-root-format linux the default option.

Describe alternatives you've considered

Find and replace, which is a tad tedious and impossible to enforce in a team of developers.

Start by reproducing the openapi-generator generate command with schemas/algorithms.yaml and the markdown generator on Linux and Windows, then trace how docs/@api/algorithms/README.md builds the Models link. Done means the generated link format is consistent across operating systems, with the compatibility/default behavior decided and covered by a regression test.