[SIEM] Add link to ML docs within Anomaly Detection UI

[spong]

Currently we don't have any links out to ML docs from within the Anomaly Detection UI within SIEM. Adding a link to the existing copy that points to the main SIEM Machine Learning page would be beneficial as it provides additional details around how long a job looks back when started, what pre-built jobs are included, and all sorts of goodness around optimizing anomaly results.

Current UI where the Machine Learning link goes to the ML App:

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)