Support LessThanUsual machine learning alert type

[joshuafleck]

Hello, I wanted to make use of the LessThanUsual machine learning alert type, per https://coralogix.com/docs/machine-learning-metric-alert/

I get the following error at the moment when I try to use it: Unsupported value: \"LessThanUsual\": supported values: \"More\", \"Less\", \"MoreThanUsual\"

Could you please build in support for this?