[feat] improve mergeable param or add a paramater for Has/Needs code review

[himynameisdave]

The mergeable parameter is pretty good, however there is one limitation with it. It will pass (when True) if all of the checks pass, however there may be other things blocking merging (specifically it may require review). See below:

It would be good to either:

1. Update mergeable to account for this.
2. Add a new param for has/needs code review.

I think if we wanted to do number 1, we could maybe read MergeableState instead so that we actually check that the PR is indeed in a clean state. I also found this Enum which I don't see in the API library so not sure if we have access to that.