Data lifecycle docs: Advanced settings and screenshots

[kilfoyle]

I think this is mostly for Configure a lifecycle policy, but maybe elsewhere in those pages as well.

• The ILM configuration screenshots don't show that you need to expand Advanced settings.

• We don't explain the Advanced settings for each phase:

  • shrink
  • force merge
  • downsample
  • read only
  • data allocation
  • index priority

[kilfoyle]

The Create lifecycle policy section now has screen captures with the advanced settings shown and it describes the steps for both the API and UI. The advanced settings are shown in the screencaps.

For the phase actions, we now link to index lifecycle actions page, which in a separate PR has been expanded to provide descriptions of all the phases, and a table of which action is available in which phase.

We also provide an example of enabling the downsampling action with it's options (with a graphic showing the option enabled).

Closed by: #1906 and #2076