[Lens] Support for reading annotations similar to TSVB, from an Elasticsearch query

[timroes]

Users would like to add annotations to charts (see https://elastic.github.io/elastic-charts/?path=/story/annotations-lines--x-time-domain for an example). Those annotations should be based on documents from (potentially another) index in Elasticsearch.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[wylieconlon]

It would help to define the steps the user would take to add an annotation. If I were a user who was familiar with TSVB, I would expect that the "add layer" button would be the place to add an annotation.

• Configure a specific XY chart type
• Add a new layer- the new layer button would need to give you a choice:
  • Add <same chart type>
  • Add line series
  • Add annotations
• The annotation layer is only allowed to have an X axis and a "text" field

Technical requirements:

• Visualizations can support different types of layers
• A datasource that supports individual document queries

[wylieconlon]

After looking into this more and looking at what @AlonaNadler listed as priorities, this is not the highest priority annotation feature. It is a higher priority to be able to insert annotations into an XY chart, than to read from a separate index. This issue is about "read-only annotations", which are queried from Elasticsearch.

There is one main use of this feature today, which is in TSVB sample data visualizations which use the TSVB annotations feature. I don't think this is a blocker for moving to Lens in sample data.

[mbondyra]

I think this can be closed in favor of #129299