Single-sourced content for cloud and cloud icon

[nrichers]

This PR:

• Adds standard topics for spinning up the Elastic Stack on cloud and accessing Kibana, e.g.:

• Moves the various cloud attributes into a separate section to make them easier to spot:

  

• Adds some standard lead-in text you can use to point people to our Elasticsearch Service (:ess-leadin: ^^)

• Adds new cloud icons for ECE and ESS that anyone can use to indicate if something is supported on cloud

  

The content in this PR isn't intended to be the final say, but rather to create something different books can imbed now, to be reworked over time. Some improvements we should handle in the future:

• Add more single-sourced cloud tasks, e.g. for upgrading deployments
• Figure out how we can source the cloud icons out of elastic/docs without requiring --resource=$GIT_HOME/docs/ for every book (or the conf.yaml equivalent)
• If the previous bullet is addressed, to stop using the cloud icons stored on S3

Sample usage for single-sourced content is described in the source files themselves and will also be highlighted in the cloud-first writing guidelines we're working on.

[gtback]

@nrichers you can use include::{docs-root}/shared/cloud/ess-getting-started.asciidoc[] rather than traversing up and out of the current book with {asciidoc-dir}.

Like @bmorelli25 said, I think the warning about being unable to generate a header link is because the heading is in the shared file, not in the book:

source_location.path doesn't work for relative includes outside of the base_dir which we use when we build books from many repos.

I'm sure we can adapt that to work with shared-reuse snippets like this that we want to include in the main docs repo, if we decide that we want to keep the headers in the shared content, rather than everywhere that content is used.

[nrichers]

@nrichers you can use include::{docs-root}/shared/cloud/ess-getting-started.asciidoc[] rather than traversing up and out of the current book with {asciidoc-dir}.

Excellent suggestion, thank you! I changed to using {docs-root}.

Like @bmorelli25 said, I think the warning about being unable to generate a header link is because the heading is in the shared file, not in the book

It turned out to be caused by my use of a delimited block, which could cause issues if you were already inside of one when imbedding the file or if you were inside a partintro. (Moral of the story: keep things as simple as possible.)

[karenzone]

Tested the piece I need, and it LGTM

[gchaps]

LGTM