[BUG][KOTLIN] Request parameters in Kotlin client are not 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?

Description

Path parameters are not URL encoded for the Kotlin generator.

openapi-generator version

5.2.1

OpenAPI declaration file content or url

openapi: '3.0.1'

info:
  contact:
    email: test@test.com
    name: test
    url: http://test.com
  description: test
  license:
    name: "UNLICENSED"
  title: test
  version: test

servers:
  - url: "http://localhost"

paths:
  /test/{parameter}:
    post:
      summary: test
      operationId: test
      parameters:
        - name: parameter
          in: path
          required: true
          schema:
            type: string
          example: test/value
      responses:
        '200':
          description: OK

Generation Details

openapi-generator-cli generate -g kotlin -i temp.yaml

Steps to reproduce

Call the API with

DefaultApi().test("first/second")

which will call the API with POST /test/first/second instead of POST /test/first%2Fsecond.

Similarly, if I encode the parameter manually (DefaultApi().test("first%2Fsecond")), the % is escaped instead.

It seems the entire path is encoded as a whole instead of each parameter.

Related issues/PRs

Suggest a fix

Specifically the generated code

return RequestConfig(
    method = RequestMethod.POST,
    path = "/test/{parameter}".replace("{"+"parameter"+"}", "$parameter"),
    query = localVariableQuery,
    headers = localVariableHeaders,
    body = localVariableBody
)

is the problem. The parameter is replaced as is, while it should be URL encoded.

URL encoding of path parameters should be added for each parameter, not for the path as a whole.

Start with the generated Kotlin DefaultApi request construction shown in the issue and reproduce it using the provided OpenAPI YAML, generation command, and test call. Trace how the path parameter is substituted and verify that a value such as "first/second" becomes "first%2Fsecond" without double-encoding an already encoded value. Done means generated Kotlin clients URL-encode each path parameter correctly.