Add asset caching

[448-OG]

• Add asset caching using HTTP headers
• Check validity of CDN caching tools for both push and pull, checking whether there is a unified protocol for this, if not add a way to point the CDNs to assets for the url in settings

Note that axum server decides how the caching is handled, if caching is CDN based or not, for example:

use axum::{
    response::{Html, IntoResponse},
    http::header,
};

async fn ssr_handler() -> impl IntoResponse {
    let html = render_ssr_html();

    (
        [
            (header::CACHE_CONTROL, "no-store"),
            (header::PRAGMA, "no-cache"),
        ],
        Html(html),
    )
}

use tower_http::services::ServeDir;

let assets = ServeDir::new("assets")
    .precompressed_gzip()
    .with_cache_control("public, max-age=31536000, immutable");

Router::new().nest_service("/assets", assets);