docs(ec2): add ec2 connect details to arch_features.md (#5652)

## Problem


## Solution


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Author: Hweinstock

docs/arch_features.md

@@ -39,6 +39,13 @@ For connecting a new VSCode _terminal_, remote connect works like this:
 1. Toolkit [builds a session-manager-plugin command](https://github.com/aws/aws-toolkit-vscode/blob/c77fc076fd0ed837d077bc0318716b711a2854c8/packages/core/src/ecs/util.ts#L92-L104) and [passes it to a new VSCode Terminal](https://github.com/aws/aws-toolkit-vscode/blob/c77fc076fd0ed837d077bc0318716b711a2854c8/packages/core/src/ecs/commands.ts#L141-L147).
 1. VSCode displays the terminal, so the user can enter shell commands on the remote machine.
 
+For EC2 specifically, there are a few additional steps:
+
+1. If connecting to EC2 instance via remote window, the toolkit generates temporary SSH keys (30 second lifetime), with the public key sent to the remote instance.
+    - Key type is ed25519 if supported, or RSA otherwise.
+1. If insufficient permissions are detected on the attached IAM role, toolkit will prompt to add an inline policy with the necessary actions.
+1. If SSM sessions remain open after closing the window/terminal, the toolkit will terminate them on-shutdown, or when starting another session to the same instance.
+
 ### Implementation of remote connect
 
 These modules show how to use and extend the "remote connect" functionality: