Align the introductory and feature tier material between solutions #2629
Description
We should align how we introduce our solutions. Currently, Observability has a "What is Elastic Observability" section that I don't believe other solutions have.
Right now this page is feature oriented, but the addition of serverless and feature tiers, it could also focus on deployments and tiers.
We also need to discuss how we document feature tier documentation, and how we can make it easier for users to find this information. It's currently spread across a few pages, and we might be able to either align that better or make it more accessible from our solution docs.