Add a filter for merged, closed, open

[djpilla95]

I just noticed an organization I'm apart of is using your Action. It's a great action and it's generating extremely useful data! Well done!
However, for us we do payouts (non-monetary) based on the work the developer merges in for a given month. I just noticed that a developer is being shown to have huge contributions even though it's for a closed PR that's unmerged. Therefore, they shouldn't get credit for it.

It would be helpful if there was an option to filter out unmerged PRs.

[AlexSim93]

I will think about excluding unmerged PRs from additions/deletions and PR sizes. Right now, you can use this techniques.

1. Filter in github all unmerged PRs. You can use is:unmerged in your filters
2. Create label for such PRs. For example, unmerged.
3. In my github-action add this label(unmerged) to EXCLUDE_LABELS parameter

Actually it will filter out all unmerged PRs from the report. I am not sure if you are looking for filtering it out from all tables or just from additions/deletions column