use @generated mark in files created by sea-orm-codegen (#2199)

This makes it easier for external tools to identify these files as
generated and treat them differently according to their own
configuration.

sea-orm-codegen/src/entity/writer.rs

@@ -330,7 +330,7 @@ impl EntityWriter {
     pub fn write_doc_comment(lines: &mut Vec<String>) {
         let ver = env!("CARGO_PKG_VERSION");
         let comments = vec![format!(
-            "//! `SeaORM` Entity. Generated by sea-orm-codegen {ver}"
+            "//! `SeaORM` Entity, @generated by sea-orm-codegen {ver}"
         )];
         lines.extend(comments);
         lines.push("".to_owned());