[Docs] Logstash should have an SSL/TLS explainer docs page

[robbavey]

The Elasticsearch documentation has a useful page, breaking down support for SSL/TLS and how the different versions of the JDK influence that. With the ongoing effort to support TLS 1.3, there are a number of plugins with the same documentation snippets, which would need to be mass updated in the event of any updates/changes. A central documentation point where plugins can point to, in the same vein as the Elasticsearch docs, would help maintainability and allow us to be more comprehensive in our documentation without dominating the individual plugin docs

[karenzone]

Ideally, we can give people basic, high-level info in the plugin doc with a link to the page you're proposing. I'm thinking shared attributes. I'll look into some options.