[7.x] Http Client multipart request #32058

[ljjackson]

This PR fixes #32058.

The issue has been raised because currently multipart requests can only be sent with the full multipart form parameters, like below:

<?php

use Illuminate\Support\Facades\Http;

Http::asMultipart()->post($url, [
   ['name' => 'key', 'contents' => 'value']
]);

This is not currently in line with the sending post requests via another bodyFormat, so this PR allows for both possibilities.

<?php

use Illuminate\Support\Facades\Http;

$file = fopen($path_to_file, 'r');

Http::attach('file', $file)->post($url, [
   ['name' => 'key', 'contents' => 'value'],
   'another_key' => 'value'
]);