Add anomaly scores in anomaly detection methods

[d-a-bunin]

Description

There is no way to see anomaly score for each anomaly point. The current way to do this is to run multiple anomaly detections with different values for parameter responsible for sensitivity of detection (e.g. threshold).

Thoughts

• I'm not sure it could be implemented for all the possible anomaly detection methods. May be there are methods without sensitivity parameters.
• It seems like it could be implemented only by changing function return type
• It seems like it could be implemented by adding some new parameter similar with index_only

Related

• Add parameter `segments` for anomaly detection methods #360