[FEATURE] Share images from API to clients

[mykolasolodukha]

Definitions:

• electro - this framework.
• API Server - any project/re pository that uses electro framework in the API mode (the only available mode right now).
• Clients - any Discord/WhatsApp/Website/etc. clients that connect to the API and serve as a middleware between the API server and the platforms. Platforms = Discord, WhatsApp, etc.

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What?

• Whenever the API server wants to send an image to a Client (e.g. WhatsApp client), it sends an URL of that image as a field in the types.MessageToSend schema.

Why?

• So that we can share images (and files) from the API Server to the clients.
• Later we can have something similar be done in the other direction: whenever a User sends an image to the WhatsApp client, the Client uploads that image to a specific endpoint in the API, API returns the URL, and then the Client sends that URL as a part of the types.Message payload.

How?

• Whenever an Image needs to be sent to the Client, it first needs to be uploaded to an S3/AzureBlobStorage instance using await universal_image_storage.upload_image(...) from ./electro/toolkit/images_storage/universal_image_storage.py.
• To cover all the cases when an image/file needs to be shared, we can look at all the FilesMixin()._get_files_to_send() method from ./electro/flow_step.py. By looking at all the classes inherited from FilesMixin we can see how the method is being used.

Anything else?

• The image URL should ideally be a presigned URL. If that's not possible to achieve for AzureBlobStorage, we can ignore it. It is acceptable to have images URLs be public as long as they're not easily guessable.