fix(config): add missing enum constructors for `shared_subscription_strategy`
Currently, there's [code](048afa6d2d/apps/emqx/src/emqx_shared_sub.erl (L270-L279)) and tests that expect the possibility of
values `sticky`, `hash_topic` and `hash_clientid` in the
`node.shared_subscritpion_strategy` configuration, but the schema enum
does not contain those constructors.
There's also a `hash` constructor expected, but apparently it's just for backwards compatibility (same as `hash_clientid`), so maybe we can skip it in 5.0
3fc8d4049f