main: Stop http server

Currently it's not stopped at all, so calling a REST request shutdown-time
may crash things at random places.

Fixes: #5702

But it's not the end of the story. Since the server stays up while we are
shutting things down, each subsystem should carefully handle the cases when
it's half-down, but a request comes. A better solution is to unregister
rest verbs eventually, but httpd's rules cannot do it now.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

main.cc

@@ -710,6 +710,9 @@ int main(int ac, char** av) {
             }();
             supervisor::notify("starting API server");
             ctx.http_server.start("API").get();
+            auto stop_http_server = defer_verbose_shutdown("API server", [&ctx] {
+                ctx.http_server.stop().get();
+            });
             api::set_server_init(ctx).get();
             with_scheduling_group(maintenance_scheduling_group, [&] {
                 return ctx.http_server.listen(socket_address{ip, api_port});