Add support for delete_searchable_snapshot to ILM delete phase

[dakrone]

Describe the feature:
In Elasticsearch, the ILM delete action supports a parameter named delete_searchable_snapshot which allows a user to keep a snapshot after the index has been deleted. We're currently missing this in the UI:

It would be useful to allow a user to set this from with the UI, instead of requiring the API.

Documentation: https://www.elastic.co/guide/en/elasticsearch/reference/8.13/ilm-delete.html

Describe a specific use case for the feature:
Users would like to keep a copy of the data after it's been deleted out of the cluster, in case they want to mount it as a searchable snapshot at a later time.

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)