ECS tooling re-use enhancements

[kgeller]

Purpose

Adding some potential nice-to-have's to the way ECS currently implements re-uses.

Background

When working on https://github.com/elastic/ecs/issues/1736 , it became clear that, while our tooling is great at what it does, there are some things that could be done to enhance the way we display certain things about re-uses.

1) We don't set a default type for re-use objects i.e. process.parent like we do for regular object types like threat.enrichments.indicator. 2) Connect the dots between ^ and https://github.com/elastic/ecs/pull/1838 so that when we list re-uses to be arrays, that we see that come through in the generated artifacts, kind of like https://github.com/elastic/ecs/blob/main/generated/csv/fields.csv#L162

Potential question(s)

• Do we want to default to object, or do we care to specify something like 'flattened'?
• Do we want to somehow bubble that we expect an array to the beats artifacts like here?

Note: https://github.com/kgeller/ecs/tree/reuse-array-support contains some startings of trying to work through the above

[ebeahan]

Also could explore including some sort of field filtering for reuses here.