[Feature Request] Send view-once image, video, and voice messages

Is your feature request related to a problem? Please describe.

WAHA does not provide a documented first-class API for sending media using WhatsApp's native "view once" mode.

This is important for privacy-sensitive workflows where sending the same image, video, or voice message as ordinary persistent media is not an acceptable substitute.

Existing issues #1634 and #1972 discuss detecting or receiving view-once messages. This request is specifically about sending them.

Describe the solution you'd like

Add a normalized option for supported media endpoints, for example:

{
  "session": "default",
  "chatId": "[email protected]",
  "file": {
    "mimetype": "image/jpeg",
    "url": "https://example.com/image.jpg"
  },
  "viewOnce": true
}

The option could be added to sendImage, sendVideo, and sendVoice, or exposed through a dedicated endpoint if that better matches WAHA's architecture.

WAHA should:

• validate whether the media type and selected engine support view-once sending;
• send the native WhatsApp view-once message instead of simulating deletion;
• return the standard message ID and indicate that view-once mode was applied;
• reject unsupported combinations clearly instead of silently sending persistent media;
• document engine-specific support.

Describe alternatives you've considered

• Sending ordinary media and deleting it later: not equivalent, because the recipient may retain or reopen the media before deletion.
• Sending a temporary external download link: different user experience, trust model, and privacy behavior.

Additional context

Suggested acceptance criteria:

• The recipient sees the native WhatsApp view-once indicator and can open the media only according to WhatsApp's native behavior.
• Existing media endpoints remain unchanged when viewOnce is omitted or false.
• Unsupported engines or media types return a clear validation/unsupported-operation error.
• OpenAPI documentation, examples, and the engine feature matrix are updated.

Related: #1634, #1972