[BUG][typescript-axios] 'isCollectionFormatMulti' flag not being set to true on multiple file uploads

Created by: BrMtssk

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

I have the exact use case as described on #7247 (closed) for uploading multiple files, but apparently the 'isCollectionFormatMulti' is not set to 'true' on those cases and therefore the generator still handle those parameters as strings.

openapi-generator version

Latest master (3de53706)

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: test
  version: "1.0.0"
tags:
  - name: test
    description: test
servers:
  - url: http://localhost:3000
paths:
  /api/upload:
    post:
      tags: []
      operationId: upload files
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                message:
                  type: string
                files:
                  type: array
                  items:
                    type: string
                    format: binary
              required:
                - message
      responses:
        200:
          description: ok

Generation Details

openapi-generator-cli.jar generate -i foo.yaml -g typescript-axios -o foo

Steps to reproduce

Generate the client via the above command. Verify that the output contains the following lines:

if (files) {
    localVarFormParams.append(files.join(COLLECTION_FORMATS.csv));
}

The desired output should be

if (files) {
    files.forEach((element) => {
        localVarFormParams.append('files', element as any);
    })
}

Related issues/PRs

#7247 (closed) #7814

Suggest a fix

Correctly set the flag to true on postProcessParameter. I am going to submit a PR addressing it.