[Meta] Legacy editors deprecation plan

[teresaalvarezsoler]

We are aiming to deprecate and fully remove the legacy editors (TSVB and Aggregation based -including Timelion-) in version 10.0 (~2.5 years from now) assuming users can replace their visualizations with Lens that should support any key missing features by then.

This is a meta issue to track all the tasks that need to happen:

• [ ] https://github.com/elastic/kibana/issues/191489
• [ ] https://github.com/elastic/kibana/issues/197045
• [ ] https://github.com/elastic/kibana/issues/197702
• [ ] Identify and agree on a list of key missing features that need to be added into Lens or Dashboards
• [ ] Design a migration strategy to Lens
• [ ] Implement key missing features
• [ ] Implement migration strategy
• [ ] Show a deprecation badge each time a visualization is open in edit mode letting users know the deprecation date
• [ ] Remove legacy editors

[elasticmachine]

Pinging @elastic/kibana-visualizations (Team:Visualizations)