Remote clusters: ECE -> ECK referencing steps of a procedure of another doc

[eedugon]

Affected document: https://www.elastic.co/docs/deploy-manage/remote-clusters/ece-enable-ccs-for-eck

This approach is not ideal:

The equivalent doc of Remote Clusters from ECH to ECK doesn't face this issue as we recently updated it.

We should write a clear and valid procedure instead of linking to N steps of another do that could eventually change.

Consider using snippets if the procedures of both pages are really equivalent or similar.