rgw: be compatible with fmtlib v8

rgw: be compatible with fmtlib v8

before fmtlib v9, fmtlib provides:

template<typename S, typename ...Args, typename Char = enable_if_t<detail::is_string<S>::value, char_t<S>>>
void fmt::print(std::basic_ostream<Char> &os, const S &format_str, Args&&... args)

but in fmtlib v9 and up, it provides:

template<typename ...T>
void fmt::print(std::ostream &os, format_string<T...> fmt, T&&... args)

so we need to use different function signatures for talking to different
fmtlib versions.

please see
https://fmt.dev/8.1.0/api.html#_CPPv4I0Dp0EN3fmt5printEvRNSt13basic_ostreamI4CharEERK1SDpRR4Args,
and
https://fmt.dev/9.0.0/api#_CPPv4IDpEN3fmt5printEvRNSt7ostreamE13format_stringIDp1TEDpRR1T

fore more details.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>