repair: add fmt::formatter for repair_hash

before this change, we rely on the default-generated fmt::formatter created
from operator<<, but fmt v10 dropped the default-generated formatter.

in this change, we define formatters for repair_hash.

Refs #13245

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

repair/hash.hh

@@ -2,6 +2,7 @@
 #include <absl/container/btree_set.h>
 #include <cstdint>
 #include <ostream>
+#include <fmt/core.h>
 #include "schema/schema.hh"
 
 class decorated_key_with_hash;
@@ -40,4 +41,8 @@ public:
     repair_hash do_hash_for_mf(const decorated_key_with_hash& dk_with_hash, const mutation_fragment& mf);
 };
 
-
+template <> struct fmt::formatter<repair_hash>  : fmt::formatter<std::string_view> {
+    auto format(const repair_hash& x, fmt::format_context& ctx) const {
+        return fmt::format_to(ctx.out(), "{}", x.hash);
+    }
+};