[Discover] Show ECS field descriptions in Discover, like Security app

[gbanasiak]

Describe the feature:

Security app shows index field descriptions taken from ECS schema, example for 7.12.0:

Descriptions are not present for fields copied from source indices (if not part of ECS schema).

Request:

• provide a way to add descriptions for custom fields outside of ECS schema
• extend display of field descriptions to Discover

Describe a specific use case for the feature:

Easier inspection of custom data.

[elasticmachine]

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

[wylieconlon]

Related issues:

• Lens use of ECS [Lens] Use ECS schema information in field browser and suggestions #55898
• Lens display metadata on fields [Lens] Show mapping meta information in field info popover #95551

[ebeahan]

@gbanasiak this sounds amazing!

provide a way to add descriptions for custom fields outside of ECS schema

We have some tooling around ECS that helps users manage their custom fields alongside ECS. Would be awesome to expand that support to this type of feature.

cc @elastic/ecs

[timroes]

I don't think we should tie that specifically to ECS in Discover, since it's a general purpose tool, but instead we should be able to show field descriptions in general, so that we can show helpful descriptions to whatever the users added as information to the fields. We're currently not loading them into index patterns unfortunately. I've created #98873 to track this.

[jughosta]

Linking to #89726

[kertal]

Since we now have a field fields metadata service this could be implemented #183806, so if no description is DataView Field Description is provided, we can use this new service to provide ECS description information