[BUG] [rust-server] Multipart requestBody camelCase property names are mangled to snake_case

Description

Multipart requestBody property names that are in camelCase are mangled so that the generated server expects the snake_case version in requests.

openapi-generator version

6.0.1

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: TestAPI
  version: 1.0.0
paths:
  /the/endpoint:
    post:
      operationId: testOp
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              required:
              - camelCase
              - file
              properties:
                camelCase:
                  type: string
                file:
                  type: string
                  format: binary
            encoding:
              camelCase:
                contentType: text/plain
              file:
                contentType: image/png
        required: true
      responses:
        200:
          description: Success
          content:
            application/json:
              schema:
                type: string

Command line used for generation

openapi-generator generate -g rust-server --enable-post-process-file --generate-alias-as-model

Steps to reproduce

1. cargo run --example server
2. curl -v -F camelCase=test -F file=@<test file> http://127.0.0.1:8080/the/endpoint

Suggest a fix/enhancement

Generated code works if the generated if "camel_case" is replaced by "camelCase" in the the line

let field_camel_case = entries.fields.remove("camel_case");

but the mangled name also occurs in generated error messages.

Generate the rust-server example from the supplied OpenAPI declaration and run cargo run --example server, then reproduce the request with the documented curl command. Start at the generated let field_camel_case = entries.fields.remove("camel_case"); line and trace the related error messages; done means multipart requests use the declared camelCase property name throughout.