bug: mcp-remote should support custom authentication headers/flows for AWS-deployed MCP servers

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue
- [x] I have run `q doctor` in the affected terminal session
- [x] I have run `q restart` and replicated the issue again

### Operating system

linux

### Expected behaviour

## Expected Behavior
mcp-remote should be able to connect to MCP servers that require authentication (like AWS Cognito JWT tokens) by supporting custom headers or auth plugins

### Actual behaviour

mcp-remote fails to connect to AWS-deployed MCP servers with error "-32002: connection closed: initialize response" because it doesn't support the required Cognito authentication flow

### Steps to reproduce

1.Deploy MCP server using AWS Solutions Guidance (https://aws.amazon.com/solutions/guidance/deploying-model-context-protocol-servers-on-aws/)
2. Configure Q CLI with: "command": "npx", "args": ["mcp-remote", "https://server-url/mcp"]
3. Server requires Cognito authentication but mcp-remote doesn't support auth headers
4. Connection fails during initialization

### Environment

```yaml

```