Documentation needed for version 0.90

[kristin-kronstain-brown]

Change log: https://github.com/kagent-dev/kagent/releases/tag/v0.9.0

Needs additional documentation:

• Agent Sandbox -- New concept page covering what sandboxes are, SandboxAgent CRD reference, setup steps (install agent-sandbox, create SandboxAgent), and network allowlists. In Docs for agent sandbox #356
• OIDC proxy auth -- Setup guide covering Helm values (controller.auth.mode, oauth2-proxy subchart config), IdP integration steps, architecture diagram (the PR has one), and NetworkPolicy behavior.
• SAP AI Core provider -- Add to supported providers list with configuration steps and Helm values.
• Token exchange for model auth -- How token exchange works, when to use it, and ModelConfig configuration.
• Bedrock embeddings -- Update the agent memory page to mention Bedrock as an embedding option. In v0.9 doc updates for bedrock embeddings, gorm, and rbac #355
• RBAC scope change (#1728) -- Update Helm values reference: rbac.clusterScoped is removed, behavior is now derived from rbac.namespaces. In v0.9 doc updates for bedrock embeddings, gorm, and rbac #355
• golang-migrate (#1561) -- Possibly update operational docs if users need to know about migration tooling changes. In v0.9 doc updates for bedrock embeddings, gorm, and rbac #355