Error occurrence count details in filters/discarded-groups/ view

### Problem Statement Using Sentry for a long time and having accumulated thousands of errors, we have over a hundred "Discarded Issues" (on `/settings/projects/<id>/filters/discarded-groups/`). Almost all of these issues were discarded because they were spammy at that time. However, today, many of these are from old releases (which no user is on) or fixed issues (which should not occur anymore), so they cannot spam much. I would like to prune this list to ensure that any new issue that occurs now and matches one in the list is not discarded (so we can fix it). However, the errors' details are too generic (as previously mentioned in https://github.com/getsentry/sentry/issues/60158). Therefore, I am not so confident in undiscarding them because I am worried about potential spam. ### Solution Brainstorm The errors are very generic, so it's hard for us to assess whether they're still spammy. If adding all the error details is not feasible, it would at least help to add these two values for each discarded issue: - date when this issue was discarded - count of events discarded in the last 30 days due to this issue Sentry already knows the total discarded count. This count is shown on the same page in a graph titled "Events filtered in the last 30 days (by day)". It would help to see the breakdown of the total discarded count for each of the "Discarded Issues". ### Product Area Ingestion and Filtering