Allow configuration of anomaly detection for Key User Actions of a dynatrace_web_application

[nmarchini]

Is your feature request related to a problem? Please describe.
The dynatrace_web_application and dynatrace_key_user_action currently allows configuration of Key User Actions by name, via a set of strings, but KUAs also support configuring individual anomaly detection for each action, which is not currently supported by the provider.

Describe the solution you'd like
We would like to be able to provide anomaly detection configuration for these KUAs in the dynatrace_web_application resource.

Describe alternatives you've considered
The only alternative we are aware of is to configure this manually and reproduce the configuration on each environment, which is difficult to maintain.

Additional context
There was a similar issue logged by mattBaumBeneva in issue #326 but for the dynatrace_mobile_application resource. A similar approach is needed for dynatrace_web_application