feat: Graceful shutdown with old web server (#2786)

- Stop accepting connections during graceful shutdown in the old web server
- Stop all the services before Clio exits
- Move cache saving into stop callback

src/web/interface/Concepts.hpp

@@ -22,6 +22,7 @@
 #include <boost/beast.hpp>
 #include <boost/beast/core/error.hpp>
 
+#include <concepts>
 #include <memory>
 #include <string>
 
@@ -39,4 +40,14 @@ concept SomeServerHandler =
         { handler(req, ws) };
     };
 
+/**
+ * @brief A tag class for server to help identify Server in templated code.
+ */
+struct ServerTag {
+    virtual ~ServerTag() = default;
+};
+
+template <typename T>
+concept SomeServer = std::derived_from<T, ServerTag>;
+
 }  // namespace web