[ML] Increase Test Coverage 8.18.0

[peteharverson]

Follow up to #197420

Meta issue to summarize improvements to test coverage for 8.18.0.

Jest unit tests

• [ML] Trained Models: Optimize trained models Kibana API #200977 (DA)
• [ML] Anomaly Explorer: Fixes handling of job group IDs when opening from dashboard panels  #203224 (RJ)
• Trained models NER test [ML] EUI Visual Refresh (tokens) #203518 (WR)
• Transform health alerting rule [ML] Transforms: Support wildcards in the alerting rule flyout #204226 (DA)
• [ML] Transforms: Improve messages for recovered alerts  #205721 (DA)
• Return populated fields from a data view [ML] Field Stats: Use field caps option include_empty_fields=false to identify populated fields. #205417 (WR)
• Unit tests for file upload merge tools [ML] Adding tests for file upload merge tools #209704 (JG)

API integration tests

• GET /internal/ml/trained_models_list (DA) [ML] Trained Models: Optimize trained models Kibana API #200977

Serverless tests

• Memory Usage. Check ML entities are filtered according to the project type. (RJ) [ML] Memory Usage and Notifications pages serverless functional tests #205898
• Notifications page. Check ML entities are filtered according to the project type. (RJ) [ML] Memory Usage and Notifications pages serverless functional tests #205898

Functional tests

• Attaching a log rate analysis embeddable to a case (RJ) [ML] Adds action to add log rate analysis to a case #201549

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[peteharverson]

Closing, all items planned for 8.18 have been completed.