[BUG][JAVA][Client][RestTemplate] '+' in query parameters is not properly URL-encoded

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

This is a re-occurrence of the below issue, where date-time field is not properly encoded on the + character.
https://github.com/OpenAPITools/openapi-generator/issues/644

In my humble opinion, this is actually an issue with Spring Framework, so I opened a ticket there, but it doesn't seem to be accepted as an issue on that side, so I can only think of fixing it here instead.
https://github.com/spring-projects/spring-framework/issues/31363

openapi-generator version

I've managed to reproduce it with 6.x and 7.x.
This is technically a regression, and I believe it started to happen again once Spring Framework 5.x was adopted here, since that is where they made their change to the processing of + character in particular.

OpenAPI declaration file content or url

  /pets:
    get:
      summary: List all pets
      operationId: listPets
      tags:
        - pets
      parameters:
        - name: soldAfter
          in: query
          description: If specified, only pets sold after the given date and time will be returned.
          required: false
          schema:
            type: string
            format: date-time

(copied over from original ticket)

Generation Details

Steps to reproduce

Related issues/PRs

• https://github.com/OpenAPITools/openapi-generator/issues/644
• https://github.com/spring-projects/spring-framework/issues/31363

Suggest a fix

https://github.com/OpenAPITools/openapi-generator/pull/16732

Start by reviewing the RestTemplate client generation path and the supplied /pets query parameter with date-time format. Compare the behavior described here with issues #644 and Spring Framework issue #31363, and inspect the suggested fix in pull request #16732. Done means '+' in the generated client's query parameter is encoded as expected.