[META] AD enhancment in 2.17, 2.18

[kaituo]

Checklist

• remote index: enable aggregate data from multiple cluster; enable aggregated view of multiple remote indices and local indices. [FEATURE] Enabling remote index support anomaly-detection-dashboards-plugin#856, [FEATURE] Add ability to choose multiple indices/aliases/index pattern in detector creation anomaly-detection-dashboards-plugin#855
• flattened index mapping: Many values are not flattened, making it difficult to view them on the dashboard. For instance, entity values are nested objects, and features are arrays. The requirement is to reference a feature by name and apply conditions like f1 > 3. Additionally, there is a need to perform terms aggregation on categorical fields. This will require adjustments to the mapping and the addition of new fields in the result index. [FEATURE] Flatten result index mapping for visualizing nested objects in Dashboards #1306
• missing value imputation: Support filling in zeros, last known value, fixed value. Details: [FEATURE] Support missing value imputation #1305
• Contextual launch: Contextual launch the detector page from the main dashboard, and then launch the actual logs in Discover page from detector page. [FEATURE] Contextual Launch anomaly-detection-dashboards-plugin#875
• rule-based AD: [RFC] Combining static thresholds and streaming ML modeling for anomaly detection #563

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[kaituo]

@opensearch-project/admin -- Can you please move this to our roadmap https://github.com/orgs/opensearch-project/projects/1 under 2.17?