Update/and or clarify support for slash commands and respective error handling

### Persona

Unicorn engineer trying to invoke workflows via slash commands in GitHub comments on a PR, utilizing this repo as a dependency

### Description

When errors do occur in downstream workflows/actions, specifically slash commands that invoke this repo's workflows, it would be good to have clear error messaging or handling. Different formatting of slash commands supported might need to be more explicit.

### Use Case

Repo maintainers running into an issue with invoking the e2e tests with slash commands:

https://github.com/defenseunicorns/terraform-aws-bastion/actions/runs/8344073151
https://github.com/defenseunicorns/terraform-aws-bastion/pull/115

Unclear what the supported format for calling the e2e tests are via slash commands, i.e,:
`/test all`
or
`/test make= region=`

`/test misc-tasks`

etc.

### Impact

- User experience impact

- PR merge issues

### Completion

### Additional Context