[Extensions] Hello World Extension

[kavilla]

SDK can contextualize a hello world extension within OpenSearch Dashboards.

Related to:
opensearch-project/OpenSearch-Dashboards#2608

• Create extensions namespacing in core OpenSearch Dashboards
  • New class registration
  • OpenSearch Dashboards bootstraps
  • OpenSearch Dashboards core can find extensions
  • Extension can extend core components
• Core OpenSearch Dashboards exposes to extensions to access context, life cycle, configuration service, and render
• SDK can instantiate its own client to make requests (hits its own APIs)
• SDK can interact with core extensions interfaces/services/end-points that are exposed
• SDK can build out and run a hello world extension that hosts in the same thread of OpenSearch Dashboards that has a route in the application and renders "Hello World"
• SDK can run hello world with semantic versioning of it's own
• SDK can run compiled extension by itself (without pulling down a lot of stuff to get running).
  • Target compiled down code, we might try to avoid the osd-optimizer to make stuff less difficult

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Doesn't seem to be needed to get feature parity for current state but these are core to the application and extensions so should be tracked but not blocking.

• Extensions can access saved objects, global state management, application state management