Improve action output by using workflow step summaries

### TL;DR

Use GitHub [step summaries](https://github.blog/2022-05-09-supercharging-github-actions-with-job-summaries/) to improve readability and easier viewing of outputs from guardian when run in github actions.

### Detailed design

Using step summaries, add a step summary to show the terraform command outputs (plan, apply, etc) in a streamlined format so users can see information easier in the GitHub UI, rather than digging through the output logs.

### Alternatives considered

_No response_

### Additional information

_No response_