Add missing SQL functions

[karyware]

Page: https://docs.emqx.io/en/enterprise/v4.3/rule/rule-engine.html

Add the missing SQL functions so that it is consistent with this page. For example, clientip() is missing. https://github.com/emqx/emqx/blob/master/apps/emqx_rule_engine/src/emqx_rule_funcs.erl

Also, it would be good if there were examples, especially for the functions that are not obvious.