Add status action type

[jnwng]

in discussions about what the purpose of the dryRun flag is, it was a little confusing as to what it actually does.

however, it is clear that dryRun true is the same as action: none, which i think is a little more clear in terms of "what happens when this rule passes"

[gagoar]

I've been thinking about this option. This will override the action on all the rules that have been defined. is that what you were thinking? meaning it will be at the workflow level, like dryRun.

[gagoar]

I think the best would be to add another enum to the action field in the rule, that clearly states that if the rule does not match, the step will fail. FAIL_STEP would be the value

[cyamonide]

Re: discussion with @gagoar offline, perhaps the best way moving forward here is to introduce a new action called check_required, which will trigger a failing GitHub check when the rule isn't matched. Instead of using the customMessage field to post a comment on a PR, that field would be interpreted as the error message to communicate on failure.

This new action should effectively eliminate the need of errorLevel and the none action, as described in #87.

This also begs the question of whether we should introduce a check_optional action. I argue no, since I don't see a use case for having a check_optional that doesn't have any side effects (neither triggers a failing check nor posts a message).