[manage data] Add Data tiers content

[colleenmcginnis]

Closes https://github.com/elastic/docs-projects/issues/375

Adds Data tiers content. @kilfoyle @wajihaparvez do you think this page is too long? Should I attempt to break it into smaller chunks or do you think it's ok for now?

[wajihaparvez]

@colleenmcginnis It looks great overall! I do think it's a little long, how about you move Configure data tiers (along with its six subsections) to a different page?
Considering the migration time crunch though, I also think this is ok for now and we could break this up later.

[kilfoyle]

Suggested change

Elastic Cloud Enterprise tries to move all data from the nodes that are removed during plan changes. To disable a non-searchable snapshot data tier (e.g., hot, warm, or cold tier), make sure that all data on that tier can be re-allocated by reconfiguring the relevant shard allocation filters. You’ll also need to temporarily stop your index lifecycle management (ILM) policies to prevent new indices from being moved to the data tier you want to disable.

{{ech}} and {{ece}} try to move all data from the nodes that are removed during plan changes. To disable a non-searchable snapshot data tier (e.g., hot, warm, or cold tier), make sure that all data on that tier can be re-allocated by reconfiguring the relevant shard allocation filters. You’ll also need to temporarily stop your index lifecycle management (ILM) policies to prevent new indices from being moved to the data tier you want to disable.

These "disable a data tier" steps apply for both Elastic Cloud Hosted users and Elastic Cloud Enterprise users. Thankfully the pages are pretty much identical:

• ECE version: https://www.elastic.co/guide/en/cloud-enterprise/current/ece-disable-data-tier.html
• Elasticsearch Service version: https://www.elastic.co/guide/en/cloud/current/ec-disable-data-tier.html

[colleenmcginnis]

Earlier on the page we use {{ess}} or {{ece}}. Should I replace all mentions of {{ess}} with {{ech}} or use {{ess}} and {{ece}} here? I'd like to keep it consistent.

[kilfoyle]

I would use {{ech}} (Elastic Cloud Hosted). Apparently that term is not an exact replacement for {{ess}} (Elasticsearch Service), but I think it's the best we have right now since the latter is definitely depricated.

[kilfoyle]

LGTM! 🐙
I added just a few minor comments. I agree with Wajiha that it might make sense to separate the Configuring task content onto a separate page so that it's separate from the conceptual stuff, but that might be a problem for a later day.

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Add: I'm guessing that these instructions don't apply for Serverless, so (as with some of the docs I'm working on) we'll probably need to come back to this to add the applies labeling.