fix(config): add missing enum constructors for `shared_subscription_strategy`

Currently, there's code and tests that expect the possibility of a
value `sticky`, `hash_topic` and `hash_clientid` in the
`node.shared_subscritpion_strategy` configuration, but the schema enum
does not contain those constructors.

apps/emqx/src/emqx_schema.erl

@@ -828,7 +828,7 @@ fields("broker") ->
            })
       }
     , {"shared_subscription_strategy",
-       sc(hoconsc:enum([random, round_robin]),
+       sc(hoconsc:enum([random, round_robin, sticky, hash_topic, hash_clientid]),
           #{ default => round_robin
            })
       }