[BUG][JAVA][webclient] query param of type array handled as non explode

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

Wrapping query params in a containing object so that the generated client method only has one param instead of X params, but when the query param is an array, the generated code always builds a CSV with the contents of the array, instead of handling it as "multi".

openapi-generator version

It's not a regression. Wrapping object were supported after 7.2.0 thanks to this PR but it is not working correctly when having array properties.

OpenAPI declaration file content or url

paths:
  /api/search:
    get:
      operationId: Search
      parameters:
        - name: object-param
          in: query
          required: true
          schema:
            type: object
            properties:
              someArray:
                type: array
                items:
                  type: string

• The example is an adaptation from modules/openapi-generator/src/test/resources/3_0/java/explode-query-parameter.yaml

Generation Details

Java language, WebClient library, but also with RestTemplate.

Steps to reproduce

By adapting the upper mentioned file, execute the following test
JavaClientCodegenTest.shouldProperlyExplodeWebClientQueryParameters
adding

.bodyContainsLines("queryParams.putAll(apiClient.parameterToMultiValueMap(ApiClient.CollectionFormat.valueOf(\"multi\".toUpperCase(Locale.ROOT)), \"someArray\"," + " objectParam.getSomeArray()));");

Expected would be to handle the array query param as "multi" since explode defaults to true.
Actual: it's treated as csv because the collectionFormat param is null.

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/pull/17441

Suggest a fix

Start with modules/openapi-generator/src/test/resources/3_0/java/explode-query-parameter.yaml and run JavaClientCodegenTest.shouldProperlyExplodeWebClientQueryParameters for the WebClient and RestTemplate cases. Update the handling so the someArray query parameter uses multi when explode defaults to true, then verify the generated output contains the expected parameterToMultiValueMap call.