Support for role chaining

**Is your feature request related to a problem? Please describe.**

When using a central account to deploy to sub accounts, it's necessary to configure multiple connections with access keys and assume role names.

**Describe the solution you'd like**

A solution to chain roles from primary connection to sub connection provides a convenient solution to reduce duplication of access keys. For instance, in the connection configuration, add an input field for source connection (containing user access key) and assume role arn/name which would then be assumed during task execution.

**Describe alternatives you've considered**

Separate assume role arn/name parameters can be added to each task input to achieve the same effect. However, this approach requires change to all tasks and incurs additional maintenance overhead.

**Additional context**

I can create a PR with the necessary changes if the feature is approved.

Start by locating the connection configuration and task execution paths mentioned in the issue, then trace how access keys and assume-role names are currently passed to tasks. The work is done when a source connection can assume the configured role for a sub-account without duplicating credentials or changing every task input. The payload does not name specific files or tests.

Written by the indexing model from the issue text.