Time complexity: O(N) where N is the size of the hash.
Returns all fields and values of the hash stored at
In the returned value, every field name is followed by its value, so the length
of the reply is twice the size of the hash.
Array reply: list of fields and their values stored in the hash, or an
empty list when
key does not exist.
dragonfly> HSET myhash field1 "Hello"
dragonfly> HSET myhash field2 "World"
dragonfly> HGETALL myhash