[datadog_security_monitoring_rule] Add user behavior case actions

[ggarciarom]

Add support for the user_behavior case action type, including the user_behavior_name option, in the security_monitoring_rule and security_monitoring_default_rule resource

[ecdatadog]

About the last commit on the documentation, you should modify the Description field and update the documentation (make docs) . Outside of that, it will be ok for me.