Make some Embed "media" fields optional

[unnamedd]

Description

Running the project locally, I realized some fields were not being found when decoded by Codable. Then, I checked the Bluesky documentation and noticed some fields were not mandatory. This PR aims to fix them.

Documentation for

1. Embed Images
2. Embed Videos

Error

failed to load timeline: 
CompositeSocialService.BlueskyService, 
keyNotFound(
    CodingKeys(stringValue: "aspectRatio", intValue: nil), 
    Swift.DecodingError.Context(
        codingPath: [
            CodingKeys(stringValue: "feed", intValue: nil), 
            _CodingKey(stringValue: "Index 16", intValue: 16), 
            CodingKeys(stringValue: "post", intValue: nil), 
            CodingKeys(stringValue: "record", intValue: nil), 
            CodingKeys(stringValue: "embed", intValue: nil), 
            CodingKeys(stringValue: "images", intValue: nil), 
            _CodingKey(stringValue: "Index 0", intValue: 0)
        ], 
        debugDescription: "No value associated with key CodingKeys(stringValue: \"aspectRatio\", intValue: nil) (\"aspectRatio\").", 
        underlyingError: nil
    )
)

[mattmassicotte]

Thank you so much!!