v3.4.0

feat: add IAM auth support (required for stack config templating as of atmos `1.86.2`) @korenyoni (#46)

## what

• Add IAM auth support

why

• IAM auth is required for stack config templating as of atmos 1.86.2

references

• https://github.com/cloudposse/atmos/releases/tag/v1.86.2

Notes

I am not quite sure if Configure Plan AWS Credentials should be controlled by a condition. In cloudposse/github-action-atmos-terraform-plan, it is controlled by the outputs of cloudposse/github-action-atmos-get-setting. But we cannot use that action within this composite action, as the former is specific to one stack/component, whereas the latter (this repo) is not. (EDIT: it's definitely a requirement to put that step behind a condition — https://github.com/cloudposse/github-action-atmos-affected-stacks/actions/runs/10458450730)

I've added additional outputs to config, most of which are not referenced at all. However I did this in order to be consistent with cloudposse/github-action-atmos-terraform-plan.