Rename Cluster to Deployment

[ycombinator]

In #27595 (comment) we started a discussion about renaming Cluster to Deployment in the Stack Monitoring UI. This would align with the terminology used in Elastic Cloud as well.

Please 👍 if you're in favor of this change or 👎 and comment as to why if you're not.

[elasticmachine]

Pinging @elastic/stack-monitoring

[skearns64]

+1 here.

One reason I'm in favor of this is that it better prepares the terminology for solution-first deployments, where the user doesn't think about an "ES cluster," they think in terms of an "enterprise search deployment" or "app search" or "APM/Observability" where the fact that it's an ES cluster under the covers is important, but not the first thing the user thinks about. On the Stack Monitoring side, we'll eventually want to grapple with what it means to monitor each solution - are there just extra tabs in the existing UI? A more tailored experience? Lots to think about here, though it's a longer term question.