Cross Account

**Is your feature request related to a problem? Please describe.**
In an organization, multiple teams may be isolated not only by vpc but by account.

**Describe the solution you'd like**
Allowing RES infrastructure to support connecting to instances across accounts would enable organizational flexible.

**Describe alternatives you've considered**
Deploying RES on every account, or third party DCV based platforms.

The issue names no files, tests, or entry points. Start by mapping how RES currently connects to instances within one account and identify the AWS account and VPC boundaries involved. Define the cross-account connection requirements, security model, and validation criteria before implementation.

Written by the indexing model from the issue text.