[kohttp] Introduce Request dsl builder

[doyaaaaaken]

Now we use Request.Builder() to create okhttp3.Request instance.

kohttp/src/test/kotlin/io/github/rybalkinsd/kohttp/interceptors/logging/CurlLoggingStrategyTest.kt

Line 35 in c88850f

val request = Request.Builder()

It's better to introduce Request dsl builder and write code simpler like this.

request {
            url = "https://postman-echo.com/post"
            post = requestBody {
                contentType = "application/x-www-form-urlencoded"
                body = ""
            }
}

Discussed at here.
#141 (comment)

[rybalkinsd]

Hi @doyaaaaaken thanks for posting this issue.

depends on #128 #130 130