[BUG] Kotlin multiplatform file upload incorrect

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

File uploads fail on server-side as the "file" part are missing necessary headers.

openapi-generator version

5.1.0

OpenAPI declaration file content or url

Relevant snippet below:

    "/upload": {
      "post": {
        "tags": [
          "Upload"
        ],
        "summary": "Upload log files",
        "operationId": "post",
        "parameters": [
          {
            "name": "accountId",
            "in": "query",
            "required": true,
            "schema": {
              "type": "string"
            }
          },
          {
            "name": "type",
            "in": "query",
            "required": true,
            "schema": {
              "type": "string"
            }
          }
        ],
        "requestBody": {
          "content": {
            "multipart/form-data": {
              "schema": {
                "type": "object",
                "properties": {
                  "file": {
                    "type": "string",
                    "format": "binary"
                  }
                }
              }
            }
          }
        },
        "responses": {

Generation Details

Language: Kotlin
Library: Multiplatform

Steps to reproduce

1. Run openapi-generator-cli: openapi-generator-cli generate -g kotlin -o logging-api-client -i api-docs.json -c config.yaml --library multiplatform
2. Compile generated code and attempt a file upload

Suggest a fix

I was able to modify the source for the UploadApi class to include the ContentType and ContentDisposition headers and the upload behaved as expected.

ModifiedUploadApi.kt.txt

UploadApi.kt.txt

get input provider snippet.kt.txt

Start by running the provided openapi-generator-cli command with the Kotlin multiplatform library and the supplied OpenAPI snippet. Compare the generated UploadApi class with the attached modified version and inspect the get input provider snippet; done means a multipart upload includes the required ContentType and ContentDisposition headers and succeeds on the server.