tracing::trace_state: add begin() overload for seastar::value_of given as a "request" parameter.

Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>

tracing/trace_state.hh

@@ -42,6 +42,7 @@
 
 #include <deque>
 #include <unordered_set>
+#include <seastar/util/lazy.hh>
 #include "mutation.hh"
 #include "utils/UUID_gen.hh"
 #include "tracing/tracing.hh"
@@ -152,6 +153,11 @@ private:
         _client = std::move(client);
     }
 
+    template <typename Func>
+    void begin(const seastar::lazy_eval<Func>& lf, gms::inet_address client) {
+        begin(lf(), client);
+    }
+
     /**
      * Stores a batchlog endpoints.
      *