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 `gms::versioned_value`. its
operator<< is preserved, as it's still being used by the homebrew
generic formatter for std::unordered_map<gms::application_state,
gms::versioned_value>, which is in turn used in gms/gossiper.cc.
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#17366