Add markdown styles for messages

Apple's implementation of Markdown does not fully support the things that are usually sent by discord, mostly things related to Code / Code Block. Thus, an external library was added so that it has a complete rendering of Markdown elements: [swift-markdown-ui](https://github.com/gonzalezreal/swift-markdown-ui) This PR depends on another that implements element sizes and also font sizes. https://github.com/SwiftcordApp/Swiftcord/pull/179 Images: <img width="1418" alt="Captura de Tela 2023-10-17 às 17 18 12" src="https://github.com/SwiftcordApp/Swiftcord/assets/3859282/e1b8f310-3c86-44fb-957f-f07dd3dd631a">ends on another that implements element sizes and also font sizes. <img width="1418" alt="Captura de Tela 2023-10-17 às 17 18 05" src="https://github.com/SwiftcordApp/Swiftcord/assets/3859282/683a1f5e-53af-4b0d-9686-37a9e12981a0">