[Feature Request] Add authentication options for the repository configuration of the openapitools.json

Start with apps/generator-cli/src/README.md and apps/generator-cli/src/config.schema.json to understand the documented and validated repository options. Trace the repository configuration handling from the package entry points, then define how credentials are supplied safely, support authenticated query and download requests, and document the configuration and usage when both operations work with a private repository.

Currently it is possible to specify downloadUrl and queryUrl in the repository configuration block if a private repository should be used:

{
    "$schema": "./node_modules/@openapitools/openapi-generator-cli/config.schema.json",
    "spaces": 2,
    "generator-cli": {
        "version": "5.1.1",
        "storageDir": "./openapitools-download",
        "repository": {
            "queryUrl": "https://artifactory.mycorp.com/maven-central/select?q=g:${group.id}+AND+a:${artifact.id}&core=gav&start=0&rows=200",
            "downloadUrl": "https://artifactory.mycorp.com/maven-central/${groupId}/${artifactId}/${versionName}/${artifactId}-${versionName}.jar"
        }
    }
}

Unfortunately the artifact-storage of my organization requires login credentials and I can thus not use this option. It would be great if something like this could be added:

{
    "generator-cli": {
        "repository": {
            "queryUrl": "https://artifactory.mycorp.com/maven-central/select?q=g:${group.id}+AND+a:${artifact.id}&core=gav&start=0&rows=200",
            "downloadUrl": "https://artifactory.mycorp.com/maven-central/${groupId}/${artifactId}/${versionName}/${artifactId}-${versionName}.jar",
            "username":"",
            "password":"",
        }
    }
}

On a general note:
I think the documentation of these configuration options could be more extensive. I learned about the repository block via a comment on an issue as it is not in the README...