Allow add a comment to run

Can the `hashicorp/tfc-workflows-github/actions/create-run` action take a comment as input and add that comment to the Run in TFC.

By default this could be a link back to the GitHub action run url
`${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}`

Start with the hashicorp/tfc-workflows-github/actions/create-run action entry point and inspect how its inputs are defined and passed to TFC. Check any existing action tests or workflow examples, then verify that a supplied comment is added to the run and that the default GitHub Actions run URL is used when no comment is provided.

索引モデルが issue の本文から書いたものです。