this header was previously brought in by seastar's sstring.hh. but
since sstring.hh does not include <fmt/ostream.h> anymore,
`gms/application_state.cc` does not have access to this header.
also, `gms/application_state.cc` should `#include` the used header
by itself.
so, in this change, let's include <fmt/ostream.h> in `gms/application_state.cc`.
this change addresses the FTBFS with the latest seastar.
the same applies to other places changed in this commit.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#18193