Add statistics about closed / open issues in the last month

[Ly0n]

It would be interesting see how many good first issues have closed and created in the last month. This would allow us to measure the impact of ClimateTriage before and after the marketing together with GitHub.

[andrew]

Here's a first pass: https://ost.ecosyste.ms/api/v1/issues/climatetriage_counts

[andrew]

@Ly0n the count of issues closed is currently: "issues opened in the past month that have also been closed", maybe you want any issues that have been closed in the past month instead?

[andrew]

infact merged doesn't make sense here as there are only issues, not pull requests, so it will always be zero