[v2][auto-prompt] Shell mode for AWS CLI auto-prompt

Similar to the [AWS shell project](https://github.com/awslabs/aws-shell), it would be nice to have a persistent "shell" option for AWS CLI auto-prompt mode. The rationale is that there are times when I want to run multiple CLI commands back to back, and it would be more efficient for me if I can stay in auto-prompt mode instead of having to re-run `aws` again. In terms of how this is exposed it, it would either be exposed as:

* A `shell` option for the `cli_auto_prompt` configuration variable
* An explicit `aws shell` command

For anyone interested in this feature, please +1 this original comment using GitHub reactions. If there are other rationale for why this is important for you, please comment in this issue.