Support AgentCore Runtime IAM Authentication

**Problem / Motivation**

Many enterprise users—including those using AWS-native solutions—prefer leveraging IAM permissions instead of managing custom JWT tokens. IAM-based authentication simplifies access management by:
• Using existing IAM users/roles and their credential lifecycle.
• Avoiding token distribution or rotation complexities.
• Aligning with enterprise security governance and compliance.

In the current AgentCore Runtime UI (see screenshot), IAM permissions appear selectable, but I dont see any configurations to add MCP server to mcp-gateway-registry.

**Proposal**

Support MCP server configuration with IAM role within mcp-gateway-registry.