cql3: Extend the scope of group0_guard during DDL statement execution

Currently we hold group0_guard only during DDL statement's execute()
function, but unfortunately some statements access underlying schema
state also during check_access() and validate() calls which are called
by the query_processor before it calls execute. We need to cover those
calls with group0_guard as well and also move retry loop up. This patch
does it by introducing new function to cql_statement class take_guard().
Schema altering statements return group0 guard while others do not
return any guard. Query processor takes this guard at the beginning of a
statement execution and retries if service::group0_concurrent_modification
is thrown. The guard is passed to the execute in query_state structure.

Fixes: #13942

Message-ID: <ZNsynXayKim2XAFr@scylladb.com>

test/lib/cql_test_env.cc

@@ -274,7 +274,7 @@ public:
 
         auto qs = make_query_state();
         auto& lqo = *qo;
-        return local_qp().execute_prepared_without_checking_exception_message(std::move(prepared), std::move(id), *qs, lqo, true)
+        return local_qp().execute_prepared_without_checking_exception_message(*qs, std::move(stmt), lqo, std::move(prepared), std::move(id), true)
             .then([qs, qo = std::move(qo)] (auto msg) {
                 return cql_transport::messages::propagate_exception_as_future(std::move(msg));
             });