Add CURLRequest helper methods

[natanfelles]

Description

Closes #1259

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[lonnieezell]

If we're setting json in the request, shouldn't we also set Content-Type: application/json?

[natanfelles]

It looks like it has already been done:

CodeIgniter4/system/HTTP/CURLRequest.php

Lines 698 to 705 in 3d3cb5e

	// JSON
	if (isset($config['json']))
	{
	// Will be set as the body in `applyBody()`
	$json = json_encode($config['json']);
	$this->setBody($json);
	$this->setHeader('Content-Type', 'application/json');
	}

[natanfelles]

We could update this to use the \Config\Format::getFormatter('application/json').

Allow to use a custom JSON Formatter...

[jim-parry]

I don't think there is any intent to format the JSON data. If anything, it might be stringify'd. The unit testing should make this clearer.