[EPM] Mappings and Kibana Index Patterns to support constant_keyword field

[neptunian]

EPM needs to support fields with type constant_keyword or make sure it is being handled appropriately in both the index template mappings and kibana index pattern fields. I've poked around a bit and I think mappings won't need any changes but index patterns will.

• constant_keyword - streams have been added to package datasets and will be using this type to support the new indexing strategy {type}-{dataset}-{namespace}
  • stream.type
  • stream.dataset
  • stream.namespace

https://www.elastic.co/guide/en/elasticsearch/reference/master/constant-keyword.html

[elasticmachine]

Pinging @elastic/ingest-management (Feature:EPM)

[ruflin]

I think at the moment, we can treat constant_keyword the same as keyword. Moving forward it would be nice of Kibana itself becomes support for constant_keywords. I'm wondering if there is already an issue for it 🤔