seastar::httpd::request was deprecated in favor of `seastar::http::request`
since bdd5d929891d2cb821eca25896e25ed4ff658b7a.
so let's use the latter. this change also silences the warning of:
```
/home/kefu/dev/scylladb/api/authorization_cache.cc: In function ‘void api::set_authorization_cache(http_context&, seastar::httpd::routes&, seastar::sharded<auth::service>&)’:
/home/kefu/dev/scylladb/api/authorization_cache.cc:19:104: error: ‘using seastar::httpd::request = struct seastar::http::request’ is deprecated: Use http::request instead [-Werror=deprecated-declarations]
19 | httpd::authorization_cache_json::authorization_cache_reset.set(r, [&auth_service] (std::unique_ptr<request> req) -> future<json::json_return_type> {
| ^~~~~~~
```
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
5522080f80