Update Elastic Stack overview to reflect Search AI Platform

[lcawl]

Relates to #2795

This PR revamps https://www.elastic.co/docs/get-started/the-stack to align with "Search AI Platform" terminology on sites such as https://www.elastic.co/platform.

It also updates pages that linked to that page when there were better targets.

Relevant comments from the original PR include:

• Add new Elastic intro section #2795 (review): "I think we need to spend more time explaining what our components are (in quite a bit of detail), how they fit together, and the "landscape" of elastic. also, explaining the implications of the various choices users need to make when getting started. I worry that some of the cuts that were made when repositioning this will give us fewer ledges to cling onto when trying to provide core definitions of our offerings (especially when it comes to "what is elasticsearch? what is kibana? what is fleet?")."
• Add new Elastic intro section #2795 (comment) "we still need some single place to define the stack... we need somewhere someone can see what all of the stack components do and how they fit into a deployment (and a list of what counts as a stack component)..."
• Add new Elastic intro section #2795 (comment) "we definitely need to maintain an explanation of what the stack is especially given the url of this page. I'd like a clear definition of the Search AI Platform, from how this currently reads "Search AI platform" == something built around the stack. I'd like to see more connective tissue between these two: (1) here's what the stack is in terms of all the standalone "products" which are its components
  (2) the core components when combined are the platform"
• Add new Elastic intro section #2795 (comment) "I think here we need to present Kibana not only as a set of Analytics features but also as where all solutions (and their dedicated capabilities) come to life"
• Add new Elastic intro section #2795 (comment) "Does this [Elasticsearch Clients] belong to Explore"?
• Add new Elastic intro section #2795 (comment) "Few points on this section that I think align with what Shaina said earlier: (1) in addition to visualizing, it should rather be about "exploring" than "querying". I'd rename to "Explore and visualize your data". This is also the terminology used on the website to define Kibana. I think that "Query your data" could be its own section (or not) before this one (2) we should mention solutions here too more prominently. Right now the page sounds like solutions are ways to ingest data. While they also offer dedicated analytics tools, such as Synthetics, etc."
• Add new Elastic intro section #2795 (comment) "We need to emphasize on the "AI" part of Search AI platform on this page. I think this is the place for it as this is a strategic aspect of our current offering. We could even mimic the home page of https://www.elastic.co/ and make Generative AI its own category, alongside search, obs, and security. While this use case technically belongs to the Search solution, it may be worth having a single entry for it here."
• Add new Elastic intro section #2795 (comment) "I agree we need to define the Search AI Platform. I could actually see an argument for maintaining the existing stack page, and having the new content in a separate "Platform and solutions" page"
• Add new Elastic intro section #2795 (comment) "elasticsearch does about a million more things than store data. a huuuuuge part of elasticsearch is querying and manipulating data....I think we are underselling elasticsearch functionality in both our old get started section and this new version"
• Add new Elastic intro section #2795 (comment) "kibana is not the only entrypoint for querying data. unfortunately, we are 1/10 of the way through a reorganization of the explore and analyze section, and our first step was retitling the section. however, 90% of querying and analysis is done through elasticsearch API endpoints, and kibana sits on top of it and just allows you to visualize it. kibana also acts as the UI to all of the other functionality of elasticsearch (not just solutions). you can view them as the frontend and backend of a single product. most things you can do in elasticsearch, you have some (possibly underpowered) way of doing in kibana. it also allows you to do all sorts of admin tasks like managing users."

[github-actions]

🔍 Preview links for changed docs

• deploy-manage/deploy.md
• deploy-manage/deploy/cloud-on-k8s/kibana-instance-quickstart.md
• deploy-manage/deploy/self-managed.md
• deploy-manage/production-guidance/elasticsearch-in-production-environments.md
• get-started/the-stack.md
• manage-data/data-store/manage-data-from-the-command-line.md
• reference/fleet/data-streams-scenario1.md
• reference/fleet/data-streams-scenario2.md
• reference/fleet/data-streams-scenario4.md
• reference/fleet/fleet-settings.md

More links …

• reference/fleet/migrate-auditbeat-to-agent.md
• solutions/observability/apm/apm-server-binary.md
• solutions/observability/apm/apm-server-fleet-managed.md
• solutions/observability/apm/collect-metrics.md
• solutions/observability/synthetics/analyze-data.md
• solutions/observability/synthetics/configure-projects.md
• solutions/security/get-started/elastic-security-requirements.md