Support attaching images and files in chats, file uploads

Problem/Motivation

I'm coding a new ai ckeditor plugin to allow editors to send a file (pdf or image) to mistral AI to fill the text editor with the file text content using the ocr capabilities of the language model. (https://mistral.ai/fr/news/mistral-ocr)

For this to work in a development environment, I need to be able to send files to the ai service on /files endpoint. (https://docs.mistral.ai/api/#tag/files/operation/files_api_routes_upload...)

The current implementation of the provider do not offer this possibility.

Proposed resolution

Add missing methods in MistralClient.php and MistralProvider.php files.

Remaining tasks

Provide patch or create a merge request

User interface changes

none

API changes

These two methods are available :

$file = \Drupal::entityTypeManager()->getStorage('file')
      ->load($fid);
$fileInfo = $provider->uploadFile($file, 'ocr');
$fileUrl = $provider->getFileUrl($fileInfo['id']);

File url provided by mistral can be used in a chat message.

$messages = [
      [
        'role' => 'user',
        'content' => [
          [
            'type' => 'text',
            'text' => "Extract the content of the following file. Do not add any comments and do not modify the content.",
          ],
          [
            'type' => 'document_url',
            'document_url' => $fileUrl,
          ]
        ]
      ]
    ];
$config = [
    "max_tokens" => 2048,
    "top_p" => 0.4,
];
$provider->setConfiguration($config);
/** @var \Drupal\ai\OperationType\Chat\ChatMessage $response */
$response = $provider->chat($messages, $model, [
  'vdg_ai',
])->getNormalized();
$content = $response->getText();