Add SpEL support for default values

[ThanksForAllTheFish]

With a simple application like

package com.example.demo

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RequestParam
import org.springframework.web.bind.annotation.RestController

@SpringBootApplication
class DemoApplication

fun main(args: Array<String>) {
	runApplication<DemoApplication>(*args)
}

@RestController
@RequestMapping("/test")
class TestController {
	@GetMapping
	fun test(@RequestParam(defaultValue = "#{{}}") list: List<String>) =
		list
}

and a build.gradle.kts file autogenerated from Spring Initializr plus springdoc addition as follow

implementation("org.springdoc:springdoc-openapi-ui:1.5.12")
implementation("org.springdoc:springdoc-openapi-kotlin:1.5.12")
implementation("org.springdoc:springdoc-openapi-hateoas:1.5.12")

I get the following OpenAPI definition:

{
  "openapi": "3.0.1",
  "info": {
    "title": "OpenAPI definition",
    "version": "v0"
  },
  "servers": [
    {
      "url": "http://localhost:8080",
      "description": "Generated server url"
    }
  ],
  "paths": {
    "/test": {
      "get": {
        "tags": [
          "test-controller"
        ],
        "operationId": "test",
        "parameters": [
          {
            "name": "list",
            "in": "query",
            "required": false,
            "schema": {
              "type": "array",
              "items": {
                "type": "string"
              },
              "default": [
                "#{{}}"
              ]
            }
          }
        ],
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "*/*": {
                "schema": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  }
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {}
  }
}

In particular, "default": ["#{{}}"] struck me as wrong, since fun test(@RequestParam(defaultValue = "#{{}}") list: List<String>) actually uses a SpEL expression which should convert to an empty list. Should this work out of the box or am I missing some enabler configuration?

Changing to fun test(@RequestParam(defaultValue = "#{{}}") list: List<Int>) gets even worse, as now the conversion service throws an exception that translates into org.springdoc.core.ParameterInfo : Using the following default value : #{{}}, without spring conversionService

Sample project: https://github.com/ThanksForAllTheFish/springdocspel