ec2: connection fails on older versions of OpenSSH.

## Problem
- Connection (remove-window) fails when OpenSSH < 7.6
- Logs from Amazon Linux 2 machine:
```
OpenSSH_7.4p1, OpenSSL 1.0.2k-fips 26 Jan 2017
debug1: Reading configuration data /home/hkobew/.ssh/config
debug1: Reading configuration data /home/hkobew/.ssh/bastions-config
/home/hkobew/.ssh/config line 7: unsupported option "accept-new".
```
- Looks like `accept-new` option for `StrictHostKeyChecking` is not yet supported in this version: https://serverfault.com/questions/1105812/command-line-line-0-unsupported-option-accept-new-how-to-fix-this

## Steps to reproduce the issue

Attempt connection to any EC2 instance from an Amazon Linux Machine with OpenSSH < 7.6.

## Expected behavior

## System details (run `AWS: About` and/or `Amazon Q: About`)

- OS: Amazon Linux 2
- Visual Studio Code version: 1.85
- AWS Toolkit version: 1.85
- Amazon Q version: 3.33.0
- OpenSSH 7.4

Reproduce the EC2 connection and remove-window failure from an Amazon Linux 2 machine using OpenSSH 7.4, checking the generated SSH configuration and the unsupported `StrictHostKeyChecking accept-new` option. Done means connections work on OpenSSH versions below 7.6 without producing the reported configuration error.

Written by the indexing model from the issue text.