Replace mime type "application/ron" by "text/ron" and put it in the common crate

backend/src/services/mod.rs

@@ -31,7 +31,7 @@ pub async fn ron_error_to_html(
     let response = next.run(req).await;
 
     if let Some(content_type) = response.headers().get(header::CONTENT_TYPE) {
-        if content_type == ron_utils::RON_CONTENT_TYPE {
+        if content_type == common::consts::MIME_TYPE_RON {
             let message = match body::to_bytes(response.into_body(), usize::MAX).await {
                 Ok(bytes) => String::from_utf8(bytes.to_vec()).unwrap_or_default(),
                 Err(error) => error.to_string(),