Make delta in past timestamp check configurable

## Summary The current delta is 30 days. Reports older than 30 days will show a `Discarded invalid value for parameter 'timestamp' Collapse` error and the timestamp get set to the current time. I need reports older than 30 days (but not much older) to keep the original datetime. ## Motivation The project I'm working on sometimes receives old logs, older than 30 days (usually 45 days or so). I want them to keep the original timestamp. I'm aware the original timestamp can be found at `asctime` field. But I don't want old reports to show as they were generated today. The checking is still useful in cases were the clock is way off, I just want to increase the delta. ## Additional Context If I'm not mistaken, the check can be found [here](https://github.com/getsentry/sentry/blob/d0dd8dbdff800a7b0fa544131ccc47141010c591/src/sentry/event_manager.py#L187), the current value is hard coded to 30 days.