Document AWS STS authentication feature for ToolHive users.
Cover:
- What it is: centralized AWS credential management for AWS MCP Server
- Why use it: avoid distributing AWS credentials to developer machines
- How to set it up: AWS IAM OIDC provider, trust policies, role mappings
- Configuration examples for CLI and Kubernetes operator
Depends on: stacklok/toolhive#3570
Ref: THV-0033