[Discover] Add functional tests for Discover contextual awareness framework

[davismcphee]

📓 Summary

We introduced the Discover contextual awareness framework in #184698, but it currently has no functional test coverage since no profiles have been implemented yet. We currently have a single getCellRenderers extension point available which we can use to begin adding functional tests for the framework. In order to add the tests, we should add example profiles and extension point implementations that are enabled only when running developer examples or enabling a developer feature flag (TBD based on feasibility and what works best). Further functional test coverage will be added for each actual extension point implementation as they're completed.

✔️ Acceptance criteria

• Create example profile and getCellRenderers extension point implementations to support functional testing.
• Only enable the example implementations when either running developer examples or enabling a developer feature flag (TBD).
• Include tests to validate that the framework and extension points are working at each context level (root, data source, and document).

[elasticmachine]

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