Data lifecycle docs: Create template: document data retention & add index settings example

[kilfoyle]

For the Create template UI:

• If you start from a “Create template” and enable “Data retention”, your data will be deleted after the set date. This is a new thing in the UI that isn't documented. (43:30)

• We need to provide docs with an example of what to provide for index settings. (44:00)

  • This is where you define the lifecycle policy.
  • Not covered in the docs at all. What should a user put in this field?
  • We need a screenshot and example. George mention that we've had difficulty getting the examples.
    • Zoya: put the number of replicas and the ILM policy. Can copy the example policy from the very bottom of Configure a lifecycle policy
  • We'll add a template to copy and paste.

[kilfoyle]

Completed via #1906

Configure a lifecycle policy now explains the data retention option. For the index templates settings, I've added UI steps for the whole procedure and that includes a copy-and-pastable example: