feat: get-version-from-composer-and-pass-it-in-headers

[Zaimwa9]

Contributes to #107.

---

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• I have added information to docs/ if required so people know about the feature!
• I have filled in the "Changes" section below?
• I have filled in the "How did you test this code" section below?
• I have used a Conventional Commit title for this Pull Request

Changes

• new utility getUserAgent to get version from composer as flagsmith-php-sdk/v4.5.1 or returns flagsmith-php-sdk/unknown
• Added header in API and Analytics requests

How did you test this code?

• Added tests

Use this dummy php server:

<?php

require_once __DIR__ . '/vendor/autoload.php';

use Flagsmith\Flagsmith;
use Psr\Http\Client\ClientInterface;
use Psr\Http\Message\RequestInterface;
use Psr\Http\Message\ResponseInterface;
use GuzzleHttp\Psr7\Response;

class LoggingClient implements ClientInterface
{
    public function sendRequest(RequestInterface $request): ResponseInterface
    {
        echo "\n=== HTTP REQUEST ===\n";
        echo "Method: " . $request->getMethod() . "\n";
        echo "URI: " . $request->getUri() . "\n";
        echo "\nHeaders:\n";
        foreach ($request->getHeaders() as $name => $values) {
            foreach ($values as $value) {
                echo "  {$name}: {$value}\n";
            }
        }
        return new Response(200, ['Content-Type' => 'application/json'], []);
    }
}


try {
    $flagsmith = (new Flagsmith('test-api-key'))
        ->withClient(new LoggingClient());

    echo "Getting environment flags...\n";
    $flags = $flagsmith->getEnvironmentFlags();
} catch (Exception $e) {
    echo "\n✗ Error: " . "\n";
}

This returns normally:

 Method: GET
URI: https://edge.api.flagsmith.com/api/v1/flags/

Headers:
  Host: edge.api.flagsmith.com
  Accept: application/json
  Content-Type: application/json
  X-Environment-Key: test-api-key
  User-Agent: flagsmith-php-sdk/v4.5.1

Or after removing the version in composer:

 Method: GET
URI: https://edge.api.flagsmith.com/api/v1/flags/

Headers:
  Host: edge.api.flagsmith.com
  Accept: application/json
  Content-Type: application/json
  X-Environment-Key: test-api-key
  User-Agent: flagsmith-php-sdk/unknown