[Unified Search] Comparison & opinionated controls in unified search

[ghudgins]

Describe the feature: Add "Comparison" controls to unified search (or controls more generally)

Describe a specific use case for the feature:

Extendability for Elastic solutions
When I am analyzing data in APM
I need an opinionated control that has a custom action for adding comparison windows to all APM visualizations as part of the global unified search
So I can apply a custom action (time shifts and comparison periods to many visualizations) in a single global interaction

General use case
When I am authoring a dashboard
I need to create opinionated controls that work in conjunction with unified / free form search
So I can help my users filter the data in meaningful ways without the users having to understand field names

Related issues for controls: #120035
Related issue for unified search: #126095

CC @smith @jasonrhodes @ThomThomson @teresaalvarezsoler @stratoula @cchaos - please note the discuss label. there was an action item out of the controls product review to revisit the controls + unified search design in phase 3 (which will start design soon-ish)

[elasticmachine]

Pinging @elastic/kibana-vis-editors @elastic/kibana-vis-editors-external (Team:VisEditors)

[timductive]

closing this as this decisions has been made