Add Kubernetes and Helm annotations feature documentation

[willtsai]

What content needs to be created or modified?

Today, Radius has a feature where the user may add Radius to their existing Kubernetes/Helm applications via annotations in the Kubernetes YAML files. However, the feature is not documented in any of the guides or concept pages, and only appears in the Kubernetes and Helm tutorials:

• https://docs.radapp.io/tutorials/helm/
• https://docs.radapp.io/tutorials/add-radius/

Describe the solution you'd like

The Radius supported features for Kubernetes YAML Annotations should be documented as features in addition to existing mentions in the tutorials.

Where should the new material be placed?

Suggestion is to put this content in the containers overview page.

This new content should then be cross-linked in the relevant tutorials:

• https://docs.radapp.io/tutorials/helm/
• https://docs.radapp.io/tutorials/add-radius/

The associated pull request from the Radius code repo, if applicable

n/a

Additional context