Registering an expression function to retrieve anomalies

[amitgalitz]

Description

Creates and registers an expression function to retrieve anomalies from AD as a vis-layer to be rendered on top of visualizations in OSD.

The expression function takes a detectorId argument and utilizes the date range in the context to fetch anomalies. The anomalies are then returned as vis-layer which visualize_embeddable in OSD renders onto the given visualization.

This PR is rebased on this associated detector flyout PR (#442) as it required some of the base functionality for testing. This can either be merged after that PR is finalized or this one can be refactored to be only rebased from the featureAnywhere branch.

Issues Resolved

#408

Check List

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[amitgalitz]

@ohltyler In terms of making review easier the last commit 0722825 is the one that has all the custom expression function logic. I will add tests today/tomorrow

[ohltyler]

@ohltyler In terms of making review easier the last commit 0722825 is the one that has all the custom expression function logic. I will add tests today/tomorrow

Could you create a clean branch that just includes these changes? That way it can be reviewed and merged separately and any review context won't be lost when this would inevitably have to be rebased