Added a rule function `map_to_redis_hset_args` to help preparing redis HSET (or HMSET) multi-fields values.

For example, if `payload.value` is a map of multiple data fields,
this rule `SELECT  map_to_redis_hset_args(payload.value) as hset_fields FROM  "t/#"` can prepare `hset_fields`
for redis action to render the command template like `HMSET name1 ${hset_fields}`.