Inverse Command

👋 fellow Hubber! Love this action and its versatility.

One idea that came to mind that would be helpful would be to specify an opposite/inverse of a command that would force the `continue` output to be `'false'`. Specifically I was thinking about approval workflows that happen in issues instead of PRs. Currently, this would have to be implemented with two different `github/command` steps (one for `.approve` and one for `.deny`).

Alternatively, it'd be helpful to combine them into one step:

```yaml
- name: Approve Command
id: approve
uses: github/command@vX.X.X
with:
allowed_contexts: issue
command: .approve
opposite: .deny
```

What do you think?

_Edit:_ I just realized that I probably worded this poorly. I know that further steps that check the `continue` output would not run because commenting with `.deny` would not match the expected keyword. What would probably work better would be to have a separate output that is set when the opposite command is provided.