[Discover] Add contextual awareness framework developer documentation

[davismcphee]

📓 Summary

This issue covers adding developer documentation for the Discover contextual awareness framework introduced in #183797. We can use the PR summary as the basis for the documentation, and add additional examples and code samples to guide developers in using the framework.

✔️ Acceptance criteria

• Add a README.md file in src/plugins/discover/public/context_awareness with developer documentation for working with the contextual awareness framework.
• Use the PR summary from #183797 as the basis for the documentation, expanding on or clarifying concepts as needed.
• Include code examples and best practices to teach developers how to use the framework and provide new contextually aware experiences in Discover.

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kertal]

About examples, do you mean some examples in a readme or something in /examples like https://github.com/elastic/kibana/tree/73e72b0f5e8b433c2ddd6b513e84895eacd495cd/examples/discover_customization_examples

[davismcphee]

@kertal For this issue, I mean some code examples for how to set up new providers, etc. in the readme. But the functional test work I'm doing will also add some example profiles that can be enabled for functional and dev testing, and we can reference those in the docs too.

[kertal]

thx, this makes much of sense 👍